tor-browser@ab18008350d9d158ea7cf6efda8e74e757d41e5a added `testing/web-platform/tests/tools/third_party/attrs/.git_archival.txt`. It's a template file that is filled thanks to the `export-subst` flag set in `testing/web-platform/tests/tools/third_party/attrs/.gitattributes`. However, it's a possible source for reproducibility problems. At least, it was in MB 15.0a1 (see https://gitlab.torproject.org/tpo/applications/tor-browser-build/-/issues/41440#note_3230364). Generally speaking, we might want to ignore the `export-subst` when running `git archive`.