Update CI to test under different PHP versions

.github/workflows/php-test.yml

@@ -8,12 +8,20 @@ on:
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
 
+    strategy:
+      matrix:
+        php-version: [ '8.1', '8.2', '8.3', '8.4' ]
+
     steps:
     - uses: actions/checkout@v2
 
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ matrix.php-version }}
+
     - name: Validate composer.json and composer.lock
       run: composer validate --strict
 
@@ -22,9 +30,9 @@ jobs:
       uses: actions/cache@v2
       with:
         path: vendor
-        key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
+        key: ${{ runner.os }}-php-${{ matrix.php-version }}-${{ hashFiles('**/composer.lock') }}
         restore-keys: |
-          ${{ runner.os }}-php-
+          ${{ runner.os }}-php-${{ matrix.php-version }}-
 
     - name: Install dependencies
       run: composer install --prefer-dist --no-progress