Cache composer in phpunit job

.github/workflows/ci.yml

@@ -73,19 +73,35 @@ jobs:
     steps:
     - uses: actions/checkout@v2
 
-    - name: Set PHP version
+    - name: Get Composer cache directory
+      id: composer-cache
+      run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+    - name: Set up Composer caching
+      uses: actions/cache@v2
+      env:
+        cache-name: cache-composer-dependencies
+      with:
+        path: ${{ steps.composer-cache.outputs.dir }}
+        key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-composer-
+
+    - name: Set up PHP
       uses: shivammathur/setup-php@v2
       with:
         php-version: ${{ matrix.php-version }}
         coverage: none
-        tools: composer:v1
+        tools: composer
+
+    - name: Install Composer dependencies
+      run: |
+        composer install --prefer-dist --no-suggest --no-progress --no-ansi --no-interaction
+        echo "${PWD}/mu-plugins/vendor/bin" >> $GITHUB_PATH
 
     - name: Start mysql service
       run: sudo /etc/init.d/mysql start
 
-    - name: Install dependencies
-      run: composer install
-
     - name: Install WordPress
       run: |
         bash bin/install-wp-tests.sh wporg_5ftf_test root root 127.0.0.1 trunk