Fix incorrect model<->tokenizer mapping in tokenization testing (#19872)

* Fix model-tokenizer mapping
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

tests/test_tokenization_common.py

@@ -120,8 +120,11 @@ def merge_model_tokenizer_mappings(
             tokenizer = tokenizer_mapping[configuration][0]
             tokenizer_fast = tokenizer_mapping[configuration][1]
 
+            if tokenizer is not None:
+                if configuration.__name__.startswith(tokenizer.__name__.replace("Tokenizer", "")):
                     model_tokenizer_mapping.update({tokenizer: (configuration, model)})
             if tokenizer_fast is not None:
+                if configuration.__name__.startswith(tokenizer_fast.__name__.replace("TokenizerFast", "")):
                     model_tokenizer_mapping.update({tokenizer_fast: (configuration, model)})
 
     return model_tokenizer_mapping