Without -z, cabal update clones source-repository-packages into
dist-newstyle. Restoring an older dist-newstyle cache on top of
that fresh shallow clone corrupts it ("Could not read <commit>"),
which broke the Windows and Linux 9.14 jobs after the citeproc
tag changed.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>