Fix github actions runner image

.github/workflows/php.yml

@@ -8,25 +8,24 @@ on:
 
 jobs:
   build:
-
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v2
 
-    - name: Setup nightly PHP
+    - name: Setup PHP
       uses: shivammathur/setup-php@v2
       with:
-        php-version: '7.4'
+        php-version: ${{ matrix.php }}
 
     - name: Cache Composer packages
       id: composer-cache
       uses: actions/cache@v2
       with:
         path: vendor
-        key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
+        key: ${{ runner.os }}-php-${{ matrix.php }}-${{ hashFiles('**/composer.lock') }}
         restore-keys: |
-          ${{ runner.os }}-php-
+          ${{ runner.os }}-php-${{ matrix.php }}
 
     - name: Install dependencies
       run: composer install --prefer-dist --no-progress
@@ -35,4 +34,4 @@ jobs:
     # Docs: https://getcomposer.org/doc/articles/scripts.md
 
     - name: Run test suite
-      run: composer run-script test
+      run: composer run test