Fix seq_length to align with the BLOOM paper

There is an inconsistency between the paper (https://arxiv.org/pdf/2211.05100) and the config for this model.
Page 21, Table 3 : Sequence length is 2048 not 4096.

config.json

@@ -21,7 +21,7 @@
   "num_attention_heads": 16,
   "offset_alibi": 100,
   "pretraining_tp": 2,
-  "seq_length": 4096,
+  "seq_length": 2048,
   "skip_bias_add": true,
   "skip_bias_add_qkv": false,
   "transformers_version": "4.20.0",