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/rebase.yml

@@ -5,7 +5,7 @@ name: Automatic Rebase
 jobs:
   rebase:
     name: Rebase
-    if: github.event.issue.pull_request != '' && contains(github.event.comment.body, '/rebase')
+    if: github.repository == 'velero-io/velero' && github.event.issue.pull_request != '' && contains(github.event.comment.body, '/rebase')
     runs-on: ubuntu-latest
     steps:
     - name: Checkout the latest code