Enable all -b/--by-message-id tests using git bundles

Created git bundles with commits that have Message-ID and Link trailers:
- trailers-by-msgid.bundle: Contains 2 commits with Message-ID trailers
- trailers-by-link-format.bundle: Contains 2 commits with Link trailers

These bundles were created by:
1. Cloning the base gitdir.bundle
2. Applying patches with shazam --add-message-id (or --add-link)
3. Creating bundles from the resulting commits

The test code now uses these bundles consistently with the existing
trailers-with-tripledash.bundle pattern. All 3 -b tests pass.