Fix Blog Authorship Corpus dataset
Normally, I'm expecting errors from the validation of the README file... 😅  That is:
```
=========================== short test summary info ============================
FAILED tests/test_dataset_cards.py::test_changed_dataset_card[blog_authorship_corpus]
==== 1 failed, 3182 passed, 2763 skipped, 16 warnings in 201.23s (0:03:21) =====
``` @lhoestq, apart from the dataset card, everything is OK with this PR: I tested it locally.
This PR:
- Update the JSON metadata file, which previously was raising a `NonMatchingSplitsSizesError`
- Fix the codec of the data files (`latin_1` instead of `utf-8`), which previously was raising ` UnicodeDecodeError` for some files

Close #2679.