Skip upstream-only workflows on forks

Add repository guard (github.repository == 'velero-io/velero') to
workflows that should only run on the upstream repo. This prevents
unnecessary CI runs on forks like openshift/velero where these
workflows either fail due to missing secrets/config or duplicate
fork-specific CI.

Guarded workflows: auto_assign_prs, auto_label_prs,
auto_request_review, e2e-test-kind, nightly-trivy-scan,
pr-changelog-check, pr-codespell, pr-filepath-check,
pr-linter-check, prow-action, rebase, stale-issues.

Intentionally left unguarded: pr-ci-check (useful for contributors
on forks), get-go-version (reusable workflow_call only).

Signed-off-by: Shubham Pampattiwar <spampatt@redhat.com>

.github/workflows/stale-issues.yml

@@ -5,6 +5,7 @@ on:
 
 jobs:
   stale:
+    if: github.repository == 'velero-io/velero'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/stale@v10.1.1