Revert check/renovate to ubuntu-latest — brick-build's image has no Node

brick-build's job container (opensuse/leap:16.0) has no Node.js, and
every step in check/renovate (checkout, setup-ruby, setup-node) is a
JS-based Action that needs it just to start — both runs since the
brick-build switch failed immediately, and deploy never ran because it
depends on check passing. ubuntu-latest is shared with "Gitea Runner on
Cube" (not pinned to this specific machine), but that's fine: only
deploy (a unique label held by just brick's native runner) actually
needs to land on a specific box.

.gitea/workflows/renovate.yml

@@ -8,7 +8,9 @@ on:
 
 jobs:
   renovate:
-    runs-on: brick-build
+    # 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
     steps:
       - name: Setup Node
         uses: actions/setup-node@v4