Add SVN to PHPUnit workflow for WordPress test setup

Author: pfefferle

.github/workflows/phpunit.yml

@@ -27,6 +27,8 @@ jobs:
           extensions: mysql
       - name: Install Composer dependencies for PHP
         uses: "ramsey/composer-install@v2"
+      - name: Install SVN
+        run: sudo apt-get update && sudo apt-get install -y subversion
       - name: Setup Test Environment
         run: composer setup-local-tests
       - name: Unit Testing