Replace tj-action/changed-files

[dbarbuzzi]

SUMMARY:
Replace the use of the formerly compromised tj-action/changed-files action.

TEST PLAN:
There are a couple of runs during development of the action itself which indicate the changes behave as expected:

• https://github.com/vllm-project/llm-compressor/actions/runs/13953464034 — similar to the changes in PR regarding patterns used/expected matches
• https://github.com/vllm-project/llm-compressor/actions/runs/13954383262/job/39061707849 — a slightly more comprehensive test with similar patterns, but more files touched to ensure only the desired files are considered a match

[github-actions]

👋 Hi! Thank you for contributing to llm-compressor. Please add the ready label when the PR is ready for review.

Note: This is required to complete the testing suite, please only add the label once the PR is code complete and local testing has been performed.

[tarukumar]

/lgtm