ci: Change file_diff_from_base to be dynamic (#36260)
Summary:
Changes the file_diff_from_base function to get the base reference
directly from CircleCI's pipeline variables instead of being hardcoded
to master.
cc gchanan
Signed-off-by: Eli Uriegas <eliuriegas@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36260
Differential Revision: D21144940
Pulled By: seemethere
fbshipit-source-id: ec6d1c2adcf703119bdab2a43f26a39a5fbaf71b
