set composer root (#69)

This was failing CI because the plugin is now required by
`pestphp/pest`.

Author: JonPurvis

.github/workflows/static.yml

@@ -23,6 +23,8 @@ jobs:
         coverage: none
 
     - name: Install Dependencies
+      env:
+        COMPOSER_ROOT_VERSION: 4.x-dev
       run: composer update --prefer-stable --no-interaction --no-progress --ansi
 
     - name: Style

.github/workflows/tests.yml

@@ -31,6 +31,8 @@ jobs:
           echo "::add-matcher::${{ runner.tool_cache }}/phpunit.json"
 
       - name: Install PHP dependencies
+        env:
+          COMPOSER_ROOT_VERSION: 4.x-dev
         run: composer update --${{ matrix.dependency-version }} --no-interaction --no-progress --ansi
 
       - name: Unit Tests