Tests: Make PHPstan run in 8.2, 8.3 & 8.4 (#1072)

* Add PHP [8.2,8.3,8.4] matrices to `phpstan`

* Use a pointer with `unset($this)` to make PHP 8.4 happy

.github/workflows/lint.yaml

@@ -32,14 +32,31 @@ jobs:
   phpstan:
     name: PHPStan
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        php: [8.2, 8.3, 8.4]
     steps:
       - name: Code Checkout
         uses: actions/checkout@v4
 
+      - name: Get cache directory
+        id: composer-cache
+        run: |
+          echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+
+      - name: Cache
+        uses: actions/cache@v4
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ matrix.php }}-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-composer-${{ matrix.php }}-
+
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with:
-          php-version: "8.3"
+          php-version: ${{ matrix.php }}
           extensions: bcmath, curl, gd, mbstring, mysql, openssl, pdo, tokenizer, xml, zip
           tools: composer:v2
           coverage: none
@@ -51,4 +68,4 @@ jobs:
         run: composer install --no-interaction --no-suggest --no-progress --no-scripts
 
       - name: PHPStan
-        run: vendor/bin/phpstan --memory-limit=-1
+        run: vendor/bin/phpstan --memory-limit=-1