add multisite config to the fixture site

this shouldn't need to be done every time, so we check if multisite is true and add the config if it's not true

.github/workflows/playwright.yml

@@ -399,6 +399,18 @@ jobs:
           echo "Clone the site locally and copy PR updates"
           terminus local:clone ${{ env.SITE_ID }}
           cd ~/pantheon-local-copies/"${{ env.SITE_ID }}"
+
+          if ! terminus wp "${{ env.SITE_ID }}".dev -- config is-true MULTISITE; then
+            echo "Multisite not configured yet..."
+            echo "Copying multisite application.php"
+            rm ~/pantheon-local-copies/${{ env.SITE_ID }}/config/application.php
+            cp "${{ github.workspace }}/.github/fixtures/config/application.subdom.php" ~/pantheon-local-copies/${{ env.SITE_ID }}/config/
+            mv ~/pantheon-local-copies/${{ env.SITE_ID }}/config/application.${type}.php" ~/pantheon-local-copies/${{ env.SITE_ID }}/config/application.php
+            cd ~/pantheon-local-copies/"${{ env.SITE_ID }}"
+            git add ~/pantheon-local-copies/${{ env.SITE_ID }}/config/application.php
+            git commit -m "Set up ${type} multisite config" || true
+          fi
+
           echo "Copying latest changes and committing to the site."
           rsync -a --exclude='.git' --exclude='status-*.txt' --exclude="node_modules" "${{ github.workspace }}/" .
           git add -A