fix: ignore ListBranchNamesContainingCommit ratelimit
What
Ignore the Unavailable
grpc code returned from the ListBranchNamesContainingCommit
RPC.
Why
In https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16844 we
are seeing a single user being rate limited which is by design. We are
considering Unavailable
as an error when it shouldn't be since we are
rate-limiting by design.
In https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16844 we
plan to update the error code returned by Gitaly to ResourceExhausted
but in the meantime ignore it and not page the on-call.
Reference: https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16844