cache php extensions

optimize build times by caching php extensions, particularly for 8.4/nightly which otherwise builds extensions from source each time

.github/workflows/php.yml

@@ -20,17 +20,38 @@ jobs:
           - php-version: 8.4
             experimental: true
             composer_args: "--ignore-platform-reqs"
+    env:
+      extensions: ast, grpc, protobuf
 
     steps:
+    - name: Set cache key
+      id: key
+      run: echo "::set-output name=key::$(date +'%Y-%m-%d')"
+
     - uses: actions/checkout@v3
 
+    - name: Setup cache environment
+      id: extcache
+      uses: shivammathur/cache-extensions@v1
+      with:
+        php-version: ${{ matrix.php-version }}
+        extensions: ${{ env.extensions }}
+        key: ${{ env.key }}
+
+    - name: Cache extensions
+      uses: actions/cache@v3
+      with:
+        path: ${{ steps.extcache.outputs.dir }}
+        key: ${{ steps.extcache.outputs.key }}
+        restore-keys: ${{ steps.extcache.outputs.key }}
+
     - name: Setup PHP
       uses: shivammathur/setup-php@v2
       with:
         php-version: ${{ matrix.php-version }}
         coverage: xdebug
         tools: php-cs-fixer
-        extensions: "ast, grpc, protobuf"
+        extensions: ${{ env.extensions }}
 
     - name: Validate composer.json
       run: composer validate