* ci: wait for temporal to be up before running backend tests
If we don't wait, then there are some tests that fail because temporal
isn't up yet. These tests ideally shouldn't be using the real temporal
server, but rather the test server that is spun up when e.g. using
`temporalio.testing.WorkflowEnvironment` although for the sake of
getting tests to not be flaky, this is a good enough solution for now.
