Changes proposed by this PR

Unblocks #8893

We needed to call runtime.WithRequestTimeout() in order to correctly configure the createContainer lock with a non-zero timeout. It's actually amazing that all the other tests in here also weren't failing in a similar manner.

I figured this out by putting fmt.Println statements everywhere and printing out the configured timeout. In the lock, I was seeing that it was configured with a 0s timeout. I eventually realized that we were setting the timeout on the containerd client, but not on the Garden client (which contains the containerd client), and we create the lock with the timeout from the Garden client, not the containerd client. oops!

type GardebBackend struct {
  client containerdClient // <--configured timeout in this client
  ...
  requestTimeout time.Duration // <--didn't configure timeout here using runtime.WithRequestTimeout()
}

We configure the garden client correctly in the actual code, which is why no user has ever had an issue with creating containers like we were seeing in this test suite.

Also took the time to ensure all the tests that made custom backends were setup in the same way.

Notes to reviewer

N/A

Release Note