Fix deprecation warning in linter

<https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/>

Author: carlbennett

Diff for: .github/workflows/php-linter.yml

@@ -27,7 +27,7 @@ jobs:
 
       - name: Cache Composer packages
         id: composer-cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: lib
           key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}