The go version for all master branches is defined in `default-go-version`
locally.
Note that this validation isn't added to publishing-bot directly because
we still want to give users of the publishing-bot the ability to specify
specific go versions for the master branch if they need, but we want to
explicitly disallow this for kubernetes repos.
The list of dependencies for a repo right now is equal to the list of deps
mentioned in the require directive in the repo's go.mod file.
This means that we loose all transitive deps mentioned in the replace
directive in go.mod files.
So instead use all deps mentioned in the replace directive, and prune
any extra dependencies.
Also add a test for this in verify-publishing-bot.py
