Fix typing errors in core/model_runtime (#26462)

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api/core/model_runtime/model_providers/__base/tokenizers/gpt2_tokenizer.py

@@ -15,7 +15,7 @@ class GPT2Tokenizer:
         use gpt2 tokenizer to get num tokens
         """
         _tokenizer = GPT2Tokenizer.get_encoder()
-        tokens = _tokenizer.encode(text)
+        tokens = _tokenizer.encode(text)  # type: ignore
         return len(tokens)
 
     @staticmethod