Prevent snapshot update workflow to run on main (#7842)

Turns out if you don't give the gh workflow dispatch a ref it runs it on
main, oops

.github/workflows/update_kittest_snapshots.yml

@@ -14,6 +14,7 @@ jobs:
   update-snapshots:
     name: Update snapshots from artifact
     runs-on: ubuntu-latest
+    if: github.ref_name != 'main' # We never want to update snapshots directly on main
     permissions:
       contents: write