Added workaround for pip-check-reqs issue

Details:

* pip-check-reqs 2.3.0 fails with the latest pip 21.3 because it uses internal
  pip functions one of which went away in that pip version.
  See issue adamtheturtle/pip-check-reqs#71

Signed-off-by: Andreas Maier <maiera@de.ibm.com>

.github/workflows/test.yml

@@ -161,6 +161,9 @@ jobs:
     - name: Run check_reqs
       env:
         PACKAGE_LEVEL: ${{ matrix.package_level }}
+      # TODO: Enable for all package levels again once this issue is fixed:
+      #       https://github.com/r1chardj0n3s/pip-check-reqs/issues/71
+      if: ${{ matrix.package_level == 'minimum' }}
       run: |
         make check_reqs
     - name: Send coverage result to coveralls.io