ci(sponsor-triage): select PullRequest id in search results

The search drops is:issue to include PRs, but the GraphQL selection only
had '... on Issue { id }', so PR nodes returned no id and were skipped.
Add '... on PullRequest { id }'. (Codex/Copilot review finding.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/sponsor-triage.yml

@@ -121,7 +121,7 @@ jobs:
                   const res = await github.graphql(`
                     query($q: String!) {
                       search(query: $q, type: ISSUE, first: 100) {
-                        nodes { ... on Issue { id } }
+                        nodes { ... on Issue { id } ... on PullRequest { id } }
                       }
                     }`, { q });
                   for (const node of res.search.nodes) {