Block googleapis updates on new storage-control RPCs.

[dbolduc]

A good first step to #2398.

We want to block updates to googleapis on new storage-control RPCs.

We can use a custom build.rs file to maintain the stub_tests macro.

https://github.com/googleapis/google-cloud-rust/blob/499eec5a9985d68d1d8d3186b54fcf04189630cb/src/storage-control/tests/mocking.rs#L97

Then when a new RPC is added to storage-control, we will have failing tests until the associated manual changes are made.