ci: only disable threads for gh

vitest.config.ts

@@ -22,6 +22,8 @@ export default defineConfig({
   },
   test: {
     globals: true,
+    // disable threads on GH actions to speed it up
+    threads: !process.env.GITHUB_ACTIONS,
     setupFiles: 'scripts/setupVitest.ts',
     environmentMatchGlobs: [
       ['packages/{vue,vue-compat,runtime-dom}/**', 'jsdom']