git-artifacts: don't forget to commit MINGW-packages, if needed

When building from a tag, the version in mingw-w64-git's `PKGBUILD` will
be changed as part of the build.

We already had code intending to publish that change, but we forgot to
commit it before building a Git bundle, which does not work...

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/git-artifacts.yml

@@ -315,6 +315,7 @@ jobs:
           then
             echo "::warning::Uncommitted changes after build!" >&2 &&
             git diff >&2 &&
+            git commit -s -m "mingw-w64-git: new version ($version)" PKGBUILD &&
             git bundle create "$b"/MINGW-packages.bundle main^..main
           fi)
       - name: Cache ${{env.MINGW_PACKAGE_PREFIX}}-git