Allow skipping semver checks.

We need this currently as semver check is broken and this makes it easier to unbrick the CI in the future.

.github/workflows/rust.yml

@@ -59,6 +59,7 @@ jobs:
     - uses: stellar/actions/rust-check-git-rev-deps@main
 
   semver-checks:
+    if: "!contains(github.event.pull_request.labels.*.name, 'skip-semver-checks')"
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v3