ci: switch to actions/checkout@v4

Author: carlalexander

.github/workflows/test-php.yml

@@ -17,7 +17,7 @@ jobs:
           php-version: '8.0'
           extensions: simplexml
       - name: Checkout source code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Get Composer Cache Directory
         id: composer-cache
         run: |
@@ -52,7 +52,7 @@ jobs:
             extensions: simplexml, mysql
             tools: phpunit-polyfills
         - name: Checkout source code
-          uses: actions/checkout@v2
+          uses: actions/checkout@v4
         - name: Install WordPress Test Suite
           run: |
             bash bin/install-wp-tests.sh wordpress_test root root 127.0.0.1:${{ job.services.mysql.ports['3306'] }}
@@ -81,7 +81,7 @@ jobs:
           php-version: '8.0'
           extensions: simplexml, mysql
       - name: Checkout source code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Get Composer Cache Directory
         id: composer-cache
         run: |