fix(needs-rebase): retry mergeable check on push events to catch conflicting PRs (#1240)

With maxAttempts=1, all PRs have mergeable=null immediately after a push
and are skipped. PRs that are never subsequently updated (no new commits,
no re-opens) never get rechecked. Increasing to 3 attempts (5s + 10s backoff)
gives GitHub ~15s to compute mergeability before giving up.

Signed-off-by: Paige Patton <prubenda@redhat.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/needs-rebase.yml

@@ -168,7 +168,7 @@ jobs:
               for (let i = 0; i < prs.length; i += CONCURRENCY) {
                 const batch = prs.slice(i, i + CONCURRENCY);
                 await Promise.all(batch.map(pr =>
-                  handlePR(pr.number, pr.user.login, 1).catch(e =>
+                  handlePR(pr.number, pr.user.login, 3).catch(e =>
                     core.warning(`PR #${pr.number}: unexpected error — ${e.message}`)
                   )
                 ));