chore(internal/gapicgen): fix genbot (#2721)
chore(internal/gapicgen): fix genbot (#2721)

Go tooling was failing due to inconsistencies between protoc-gen-go
versions. This was caused by #2715.

Tested locally and the Dockerfile now builds.
googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go