Fix CI warnings

Fix warnings in our CI tests.

Comments:
_The documentation is not available anymore as the PR was closed or merged._

<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.007448 / 0.011353 (-0.003905) | 0.005182 / 0.011008 (-0.005826) | 0.098718 / 0.038508 (0.060210) | 0.034594 / 0.023109 (0.011485) | 0.317301 / 0.275898 (0.041403) | 0.357800 / 0.323480 (0.034320) | 0.005860 / 0.007986 (-0.002126) | 0.004267 / 0.004328 (-0.000061) | 0.074876 / 0.004250 (0.070626) | 0.048002 / 0.037052 (0.010950) | 0.333360 / 0.258489 (0.074871) | 0.362080 / 0.293841 (0.068239) | 0.035957 / 0.128546 (-0.092589) | 0.012245 / 0.075646 (-0.063401) | 0.332970 / 0.419271 (-0.086301) | 0.050825 / 0.043533 (0.007293) | 0.313936 / 0.255139 (0.058797) | 0.340684 / 0.283200 (0.057485) | 0.106630 / 0.141683 (-0.035053) | 1.427898 / 1.452155 (-0.024257) | 1.547518 / 1.492716 (0.054801) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.296952 / 0.018006 (0.278945) | 0.515708 / 0.000490 (0.515218) | 0.004225 / 0.000200 (0.004025) | 0.000082 / 0.000054 (0.000027) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.029365 / 0.037411 (-0.008046) | 0.111142 / 0.014526 (0.096616) | 0.124414 / 0.176557 (-0.052142) | 0.185227 / 0.737135 (-0.551908) | 0.129545 / 0.296338 (-0.166793) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.403303 / 0.215209 (0.188094) | 4.044138 / 2.077655 (1.966483) | 1.803622 / 1.504120 (0.299502) | 1.615436 / 1.541195 (0.074242) | 1.703576 / 1.468490 (0.235086) | 0.706398 / 4.584777 (-3.878379) | 3.912995 / 3.745712 (0.167283) | 4.004575 / 5.269862 (-1.265287) | 2.101592 / 4.565676 (-2.464085) | 0.087280 / 0.424275 (-0.336995) | 0.012564 / 0.007607 (0.004957) | 0.508484 / 0.226044 (0.282440) | 5.089351 / 2.268929 (2.820422) | 2.269022 / 55.444624 (-53.175602) | 1.933375 / 6.876477 (-4.943102) | 2.136783 / 2.142072 (-0.005289) | 0.862624 / 4.805227 (-3.942603) | 0.172107 / 6.500664 (-6.328557) | 0.066694 / 0.075469 (-0.008775) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.172513 / 1.841788 (-0.669275) | 15.877519 / 8.074308 (7.803211) | 14.687476 / 10.191392 (4.496084) | 0.189392 / 0.680424 (-0.491032) | 0.017334 / 0.534201 (-0.516866) | 0.420201 / 0.579283 (-0.159082) | 0.418502 / 0.434364 (-0.015862) | 0.489130 / 0.540337 (-0.051207) | 0.580678 / 1.386936 (-0.806258) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.007942 / 0.011353 (-0.003411) | 0.005312 / 0.011008 (-0.005696) | 0.074684 / 0.038508 (0.036176) | 0.035952 / 0.023109 (0.012843) | 0.349672 / 0.275898 (0.073774) | 0.377157 / 0.323480 (0.053678) | 0.006399 / 0.007986 (-0.001586) | 0.005769 / 0.004328 (0.001441) | 0.074283 / 0.004250 (0.070032) | 0.053217 / 0.037052 (0.016165) | 0.342545 / 0.258489 (0.084056) | 0.383663 / 0.293841 (0.089822) | 0.037234 / 0.128546 (-0.091312) | 0.012349 / 0.075646 (-0.063298) | 0.086522 / 0.419271 (-0.332749) | 0.049888 / 0.043533 (0.006355) | 0.337686 / 0.255139 (0.082547) | 0.361564 / 0.283200 (0.078365) | 0.104902 / 0.141683 (-0.036781) | 1.478259 / 1.452155 (0.026104) | 1.576376 / 1.492716 (0.083660) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.339760 / 0.018006 (0.321753) | 0.530946 / 0.000490 (0.530456) | 0.000474 / 0.000200 (0.000274) | 0.000063 / 0.000054 (0.000008) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.029685 / 0.037411 (-0.007726) | 0.109409 / 0.014526 (0.094883) | 0.125579 / 0.176557 (-0.050978) | 0.175378 / 0.737135 (-0.561757) | 0.130672 / 0.296338 (-0.165667) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.428456 / 0.215209 (0.213247) | 4.238731 / 2.077655 (2.161077) | 2.046703 / 1.504120 (0.542583) | 1.850701 / 1.541195 (0.309506) | 1.909290 / 1.468490 (0.440800) | 0.714314 / 4.584777 (-3.870463) | 3.816056 / 3.745712 (0.070344) | 2.118567 / 5.269862 (-3.151295) | 1.348017 / 4.565676 (-3.217659) | 0.087140 / 0.424275 (-0.337135) | 0.012546 / 0.007607 (0.004938) | 0.538041 / 0.226044 (0.311997) | 5.381822 / 2.268929 (3.112893) | 2.525685 / 55.444624 (-52.918939) | 2.178659 / 6.876477 (-4.697817) | 2.381054 / 2.142072 (0.238981) | 0.844404 / 4.805227 (-3.960823) | 0.171802 / 6.500664 (-6.328862) | 0.065630 / 0.075469 (-0.009839) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.262187 / 1.841788 (-0.579600) | 16.197668 / 8.074308 (8.123360) | 15.148636 / 10.191392 (4.957244) | 0.152601 / 0.680424 (-0.527823) | 0.020238 / 0.534201 (-0.513963) | 0.420141 / 0.579283 (-0.159142) | 0.416295 / 0.434364 (-0.018068) | 0.487051 / 0.540337 (-0.053286) | 0.581942 / 1.386936 (-0.804994) |

</details>
</details>

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