Persist yarn cache (#2137)

Summary:
The time we spend on this isn't much. However, we quite often see flakiness coming from yarnpkg not responding which should hopefully be addressed by this.

Pull Request resolved: https://github.com/facebook/flipper/pull/2137

Test Plan: CI

Reviewed By: mweststrate

Differential Revision: D27461679

Pulled By: passy

fbshipit-source-id: c7144d2a8426c078f9cab2d3a94662908a03a182

.github/workflows/nodejs.yml

@@ -22,6 +22,16 @@ jobs:
       uses: actions/setup-node@v1
       with:
         node-version: ${{ matrix.node-version }}
+    - name: Get yarn cache directory path
+      id: yarn-cache-dir-path
+      run: echo "::set-output name=dir::$(yarn cache dir)"
+    - uses: actions/cache@v2
+      id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
+      with:
+        path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
+        key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-yarn-
     - name: yarn install
       run: yarn
       working-directory: ${{env.desktop-directory}}