Add check for mozjs-sys bumps

[sagudev]

Fixes #601

To avoid problems we should also enable "Require branches to be up to date before merging" in GitHub for this repo: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/about-protected-branches#require-status-checks-before-merging

Testing:

• no mozjs_sys changes: this PRs checks
• mozjs_sys changes without bump: https://github.com/servo/mozjs/actions/runs/16565592710/job/46844809943
• mozjs_sys changes with bump: https://github.com/servo/mozjs/actions/runs/16565626054/job/46844920211

[delan]

thanks for fixing this so quickly! how come only C++ changes require a version bump? do the artifacts not contain any of the rust parts of mozjs-sys?

[sagudev]

how come only C++ changes require a version bump? do the artifacts not contain any of the rust parts of mozjs-sys?

Artifacts contain compiled SM (so all C/C++ code), all glues (src/*.cpp) and generated rust bindings of them, hence I also included mozjs-sys/* in filter to catch changes to build.rs (defines how artifacts are packed) and Cargo.toml (defines bindgen version).
Rust parts are always recompiled, as they are fast enough to compile and rust does not have stable ABI.