Bump grpc to 1.38.0

Closes #3627 (closed)

We had seen Ruby deprecation warnings in relation with the grpc gem in the main application. Those will become hard failures when moving to Ruby 3, which we are looking to do. We are therefore looking to get us onto the latest version of grpc in all affected systems (gitaly-ruby, labkit, gitlab).

There is no official changelog (last entry is from 2015: https://github.com/grpc/grpc/blob/master/src/ruby/CHANGELOG.md)

Here is the compare view: https://github.com/grpc/grpc/compare/v1.30.2...v1.38.0

Updating the same dependencies in the main app looks promising so far: gitlab!65846 (merged)