chore(deps): update actions/cache action to v6

Author: renovate[bot]

.github/workflows/phpunit.yml

@@ -47,7 +47,7 @@ jobs:
         run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Cache Composer dependencies
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}