The use of "go install" is deprecated as a way of installing and running the
Mockery binary. Update the runner script to depend on an ambient version of the
tool and ensure that in CI it's installed.
Add an actions workflow that verifies that generated files are up-to-date
during a pull request. If not, give the reader instructions about what to do to
update the PR.
Checks are included for protobuf and mockery.
