Fix query_pre_attn_scalar value

See here https://huggingface.co/google/gemma-2-9b-it/commit/1937c70277fcc5f7fb0fc772fc5bc69378996e71

config.json

@@ -22,7 +22,7 @@
   "num_hidden_layers": 42,
   "num_key_value_heads": 8,
   "pad_token_id": 0,
-  "query_pre_attn_scalar": 224,
+  "query_pre_attn_scalar": 256,
   "rms_norm_eps": 1e-06,
   "rope_theta": 10000.0,
   "sliding_window": 4096,