Fix issue with error handling in ProcessGrpcServerRegistry
If there was an error loading a repository in the gRPC server, subsequent attempts to fetch the gRPC endpoint for that origin would hit an unexpected error (instead of raising the intended user code error)
This was actually a regression introduced in https://dagster.phacility.com/D7458 to aid with the release pipeline (ironically) - if that made it into the release branch it might be worth including this fix in said release.
Test Plan: New test case that was failing before
Reviewers: sashank, johann, max, alangenfeld, prha
Reviewed By: prha
Differential Revision: https://dagster.phacility.com/D7477