GitHub Actions coveralls for push request in main repo only

Due to inability to use the COVERALLS_TOKEN secret for the PRs made from forks
It's a temporary solution and will be replaced by Codecov when the tokenless upload is implemented:
    codecov/codecov-action#29

Author: Sergey Vilgelm

.github/workflows/test.yml

@@ -22,6 +22,7 @@ jobs:
       - name: Test with inv
         run: inv cover qa
       - name: Coveralls
+        if: github.repository == 'python-restx/flask-restx' && github.event == 'push'
         run: |
           pip install coveralls
           coveralls --rcfile=coverage.rc