set a token for codecov-action

It's recommended now to set a token for uploading the report to
codecov.io as per codecov/codecov-action#955

Also set fail_ci_if_error to 'true' as this action should be stable now.

Signed-off-by: Arik Hadas <ahadas@redhat.com>

.github/workflows/pull-request.yml

@@ -121,6 +121,7 @@ jobs:
       - name: Push code coverage to Codecov
         uses: codecov/codecov-action@v3
         with:
-          files: ./go/src/github.com/${{ github.repository }}/cover.out
+          file: ./go/src/github.com/${{ github.repository }}/cover.out
           flags: unittests
-          fail_ci_if_error: false # see https://github.com/codecov/codecov-action/issues/598
+          fail_ci_if_error: true
+          token: ${{ secrets.CODECOV_TOKEN }}