ci: fix hanging setup-php, wait for DB manually, add compatibility_date

- validate job needs no PHP (the package job already validates without it)
- phpunit: runner=self-hosted so setup-php does not hang under act; replace the
  unhealthy service healthcheck with a TCP wait loop
- .config/shopware-extension.yml: set compatibility_date

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.gitea/workflows/plugin-checks.yml

@@ -15,9 +15,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: shivammathur/setup-php@v2
-        with:
-          php-version: '8.3'
       - uses: actions/setup-node@v4
         with:
           node-version: '20'
@@ -63,9 +60,6 @@ jobs:
         image: mariadb:11.4
         env:
           MARIADB_ROOT_PASSWORD: root
-        options: >-
-          --health-cmd="healthcheck.sh --connect --innodb_initialized"
-          --health-interval=5s --health-timeout=5s --health-retries=20
     env:
       DATABASE_URL: mysql://root:root@database:3306/shopware
       APP_ENV: test
@@ -75,10 +69,19 @@ jobs:
         with:
           path: plugin-src
       - uses: shivammathur/setup-php@v2
+        env:
+          runner: self-hosted # non-GitHub runner (act): without this setup-php hangs
         with:
           php-version: '8.3'
           extensions: gd, intl, pdo_mysql, zip, curl, mbstring, dom, xml, fileinfo, sodium, bcmath
           tools: composer
+      - name: Wait for the database
+        run: |
+          for i in $(seq 60); do
+            (echo > /dev/tcp/database/3306) 2>/dev/null && exit 0
+            sleep 2
+          done
+          echo "::error::database service did not come up"; exit 1
       - name: Resolve plugin name
         run: |
           # plugin directory name = short class name of extra.shopware-plugin-class