Make training args fully immutable (#25435)

* Make training args fully immutable

* Working tests, PyTorch

* In test_trainer

* during testing

* Use proper dataclass way

* Fix test

* Another one

* Fix tf

* Lingering slow

* Exception

* Clean

examples/research_projects/mlm_wwm/run_mlm_wwm.py

@@ -21,6 +21,7 @@ https://huggingface.co/models?filter=fill-mask
 """
 # You can also adapt this script on your own masked language modeling task. Pointers for this are left as comments.
 
+import dataclasses
 import json
 import logging
 import math
@@ -366,7 +367,7 @@ def main():
     # If we have ref files, need to avoid it removed by trainer
     has_ref = data_args.train_ref_file or data_args.validation_ref_file
     if has_ref:
-        training_args.remove_unused_columns = False
+        training_args = dataclasses.replace(training_args, remove_unused_columns=False)
 
     # Data collator
     # This one will take care of randomly masking the tokens.