ci: downgrade undici for deno node-compat test

Deno's node:worker_threads compat shim doesn't expose
markAsUncloneable, so undici v8 fails to load.

Author: pi0

.github/workflows/ci.yml

@@ -44,6 +44,7 @@ jobs:
       - uses: denoland/setup-deno@v2
       - run: pnpm install
       - run: pnpm vitest --coverage test/deno.test.ts test/url.test.ts
+      - run: pnpm add -D undici@^7.25.0
       - run: deno run test:node-compat:deno
   tests_bun:
     runs-on: ubuntu-latest