googlecloudstorage: enable bisync integration tests

These were habitually failing at some point and ignored for that reason, but
seem to be passing now. It is possible that in the interim, the underlying issue
was resolved by another commit. If there is still an issue lurking, the nightly
tests will surely reveal it (and give us a log to look at.)

fstest/test_all/config.yaml

@@ -169,13 +169,11 @@ backends:
    remote:   "TestGoogleCloudStorage:"
    fastlist: true
    ignoretests:
-     - cmd/bisync
      - cmd/gitannex
  - backend:  "googlecloudstorage"
    remote:   "TestGoogleCloudStorage,directory_markers:"
    fastlist: true
    ignoretests:
-     - cmd/bisync
      - cmd/gitannex
  - backend:  "googlephotos"
    remote:   "TestGooglePhotos:"