👷 run yarn install in PR-title lint workflow

The script imports shared helpers from executionUtils.ts, which pulls in
undici. Install dependencies (with the setup-node yarn cache) so the
import resolves on CI.

Author: thomas-lebeau

.github/workflows/lint-pr-title.yml

@@ -17,6 +17,10 @@ jobs:
       - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
         with:
           node-version-file: 'package.json'
+          cache: 'yarn'
+
+      - name: Install dependencies
+        run: yarn install --immutable
 
       - name: Check PR title follows gitmoji convention
         env: