ci: Fix spurious rebuilds in gst-plugins-rs trigger CI
Since we must call fetch-package to ensure that we can continue even if there's no cache (or is outdated) cerbero_package_and_check() will rebuild all git recipes, incl all gstreamer recipes.
We don't want to rebuild git recipes that have already been built, so edit the cache manually to update the git commit in the "built_version" field in the recipe status.