Upgrade actions/setup-node to v4

Remove warnings about deprecated actions using node 12

Author: adamwoodnz

.github/workflows/phpunit.yml

@@ -22,7 +22,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Set up PHP
         uses: shivammathur/setup-php@v2
@@ -45,7 +45,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - name: Install NodeJS
       uses: actions/setup-node@v4