Fix `decoder_start_token_id` to correct value `50258` from `50257`

Model does not work correctly with `decoder_start_token_id` set to `50257`. For details see [my posts in discussion](https://huggingface.co/mikr/whisper-large-v3-czech-cv13/discussions/1).

config.json

@@ -18,7 +18,7 @@
   "decoder_ffn_dim": 5120,
   "decoder_layerdrop": 0.0,
   "decoder_layers": 32,
-  "decoder_start_token_id": 50257,
+  "decoder_start_token_id": 50258,
   "dropout": 0.0,
   "encoder_attention_heads": 20,
   "encoder_ffn_dim": 5120,