Updater fails for submodule commits outside the default branch #185

The updater initializes submodules with --single-branch --no-fetch. If the pinned commit belongs to a separate release branch, checkout can fail because the commit wasn’t downloaded.

The script ignores this failure, reads the wrong current version, and attempts an unnecessary update. With no actual changes, no PR is created, and the job fails with PR hasn't been created.

This happened for gdUnit 6.2.3 in this sentry-godot job.

The updater should allow fetching the pinned commit and stop if checkout fails.