Run yarn on windows first

Author: eatonphil

.github/workflows/pull_requests.yml

@@ -118,6 +118,7 @@ jobs:
       shell: pwsh
 
     # Needed so we can have ./build/desktop_runner.js and ./build/go_desktop_runner ready for tests
+    - run: yarn
     - run: yarn build-test-runner
     - run: yarn test ui --detectOpenHandles --forceExit --verbose