Replace appends with list comprehension. (#23359)

It's more idiomatic and significantly more efficient because
1) it avoids repeated `append` call that Python has to resolve on each iteration
2) can preallocate the size of the final list avoiding resizing

src/transformers/tokenization_utils_fast.py

@@ -249,10 +249,7 @@ class PreTrainedTokenizerFast(PreTrainedTokenizerBase):
         if isinstance(tokens, str):
             return self._convert_token_to_id_with_added_voc(tokens)
 
-        ids = []
-        for token in tokens:
-            ids.append(self._convert_token_to_id_with_added_voc(token))
-        return ids
+        return [self._convert_token_to_id_with_added_voc(token) for token in tokens]
 
     def _convert_token_to_id_with_added_voc(self, token: str) -> int:
         index = self._tokenizer.token_to_id(token)