Add Coveralls to GitHub Actions workflow

Based on: https://github.com/php-coveralls/php-coveralls#github-actions

Author: TimWolla

.github/workflows/phpunit.yml

@@ -23,7 +23,6 @@ jobs:
       - uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
-          coverage: none
           extensions: gmp, bcmath
           tools: composer
       - uses: actions/checkout@v2
@@ -32,4 +31,10 @@ jobs:
           echo "::add-matcher::${{ runner.tool_cache }}/php.json"
           echo "::add-matcher::${{ runner.tool_cache }}/phpunit.json"
       - run: composer install
-      - run: vendor/bin/phpunit
+      - run: vendor/bin/phpunit --coverage-clover build/logs/clover.xml
+      - name: Upload coverage results to Coveralls
+        env:
+          COVERALLS_REPO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          composer global require php-coveralls/php-coveralls
+          php-coveralls --coverage_clover=build/logs/clover.xml -v