ci: upgrade Node.js version from 18 to 20 in workflows

Author: Tmeister

.github/workflows/test-github-release.yml

@@ -23,7 +23,7 @@ jobs:
     - name: Setup Node.js
       uses: actions/setup-node@v4
       with:
-        node-version: '18'
+        node-version: '20'
         cache: 'npm'
 
     - name: Install PHP dependencies (production only)

.github/workflows/test-wordpress-deploy.yml

@@ -23,7 +23,7 @@ jobs:
     - name: Setup Node.js
       uses: actions/setup-node@v4
       with:
-        node-version: '18'
+        node-version: '20'
         cache: 'npm'
 
     - name: Install PHP dependencies (production only)

.github/workflows/wordpress-release.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Setup Node.js
       uses: actions/setup-node@v4
       with:
-        node-version: '18'
+        node-version: '20'
         cache: 'npm'
 
     - name: Install PHP dependencies (production only)