PHP - Add github auth token to composer configuration

This writes the github auth token to a config file in ~/.composer, which then uses it when downloading packages

This will help with github rate limiting, as was happening on cucumber#52

Documentation here: https://github.com/shivammathur/setup-php#github-composer-authentication

.github/workflows/test-php.yml

@@ -25,6 +25,8 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: "${{ matrix.php }}"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Discover composer cache directory
         id: composer-cache
@@ -55,4 +57,4 @@ jobs:
 
       - name: run acceptance tests
         run: make acceptance
-        working-directory: php
+        working-directory: php