Tell renovate not to try to update GitHub runners

.github/renovate.json5

@@ -27,9 +27,20 @@
       // Group upload/download artifact updates, the versions are dependent
       groupName: "Artifact GitHub Actions dependencies",
       matchManagers: ["github-actions"],
+      matchDatasources: ["gitea-tags", "github-tags"],
       matchPackagePatterns: ["actions/.*-artifact"],
       description: "Weekly update of artifact-related GitHub Actions dependencies",
     },
+    {
+      // This package rule disables updates for GitHub runners:
+      // we'd only pin them to a specific version
+      /// if there was a deliberate reason to do so
+      groupName: "GitHub runners",
+      matchManagers: ["github-actions"],
+      matchDatasources: ["github-runners"],
+      description: "Disable PRs updating GitHub runners (e.g. 'runs-on: macos-14')",
+      enabled: false,
+    },
     {
       groupName: "pre-commit dependencies",
       matchManagers: ["pre-commit"],