Cache node_modules on GH actions (#2517)

* cache node_modules on GH actions

Signed-off-by: Jari Kolehmainen <jari.kolehmainen@gmail.com>

* tweak

Signed-off-by: Jari Kolehmainen <jari.kolehmainen@gmail.com>

.github/workflows/test.yml

@@ -20,6 +20,18 @@ jobs:
         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-
+
       - run: make node_modules
         name: Install dependencies