Better CI lint for generated code

[vrongmeal]

With Go GRPC generated code, the first few lines contain information about which exact version of protoc, protoc-gen-go and protoc-gen-go-grpc is used. It's informational but with every minor update, the lint check fails.

There are two possible solutions:

1. Pin everything to a specific version: This might be extremely annoying while development
2. Ignore these lines from the diff check: Since we're checking the exact code output, and dependency versions are defined by our go.mod, ignoring these lines in the diff should be OK.