Pin check/renovate back to brick-build now that its image has Node

The runner's label-to-image mapping got repointed at Gitea's own
official runner image (docker.gitea.com/runner-images:ubuntu-latest,
has Node out of the box) — the earlier opensuse/leap:16.0 mapping for
brick-build specifically was what broke check/renovate on 2026-09-12,
not brick-build the label itself. Back to pinning both to this
machine specifically instead of whichever runner answers to the
shared ubuntu-latest label.

.gitea/workflows/renovate.yml

@@ -9,8 +9,9 @@ on:
 jobs:
   renovate:
     # Same reasoning as check's runs-on in ci.yml: brick-build's job
-    # container has no Node, which setup-node/npm below need.
-    runs-on: ubuntu-latest
+    # container now has Node (repointed at Gitea's own official runner
+    # image), which setup-node/npm below need.
+    runs-on: brick-build
     steps:
       - name: Setup Node
         uses: actions/setup-node@v4