Merge pull request #56 from CESNET/renovate/php-actions-composer-6.x

chore(deps): update php-actions/composer action to v6

.github/workflows/build_and_check.yml

@@ -25,7 +25,7 @@ jobs:
           path: /tmp/composer-cache
           key: ${{ runner.os }}-${{ hashFiles('**/composer.lock') }}
       - name: Install dependencies
-        uses: php-actions/composer@v5
+        uses: php-actions/composer@v6
         with:
           php_version: ${{ matrix.php-version }}
           version: 2