GH Actions: allow test runs to succeed on fork

As things were, test runs on forks would always fail on the "upload code coverage reports" step, as forks (justifiably) don't have access to the `CODECOV_TOKEN`.

Fixed now by updating the conditions to run that step.

.github/workflows/tests.yml

@@ -227,7 +227,7 @@ jobs:
         run: vendor/bin/phpunit
 
       - name: Send coverage report to Codecov
-        if: ${{ success() && matrix.coverage == true }}
+        if: ${{ success() && matrix.coverage == true && github.event.repository.fork == false }}
         uses: codecov/codecov-action@5a1091511ad55cbe89839c7260b706298ca349f7 # v5.5.1
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}