ci: exclude .github/ from PHP 7.4 lint + fix PHPCS allow-plugins

Agent-Session: cowork-ci-parity-20260414

.github/workflows/ci.yml

@@ -30,12 +30,15 @@ jobs:
           php-version: ${{ matrix.php }}
           coverage: none
       - name: Syntax check all PHP files
+        # Exclude .github/mu-plugins — those run on the production server (PHP 8+)
+        # and may use PHP 8+ syntax (union types etc.) that 7.4 rejects.
         run: |
           set -e
           find . -name '*.php' \
             -not -path './vendor/*' \
             -not -path './node_modules/*' \
             -not -path './.git/*' \
+            -not -path './.github/*' \
             -print0 | xargs -0 -n1 -P4 php -l > /dev/null
 
   phpcs:
@@ -52,6 +55,8 @@ jobs:
           tools: composer:v2, phpcs
       - name: Install WordPress Coding Standards
         run: |
+          # Allow the PHPCS composer-installer plugin (auto-registers standards).
+          composer global config --no-plugins allow-plugins.dealerdirect/phpcodesniffer-composer-installer true
           composer global require "wp-coding-standards/wpcs:^3.0" "phpcsstandards/phpcsutils:^1.0" --no-interaction
           phpcs --config-set installed_paths "$(composer global config home)/vendor/wp-coding-standards/wpcs"
       - name: Run PHPCS