cleanup: Fix flaky test for invalid requests

One of our tests that verifies behaviour when sending an invalid repository as input is flaky. This is because the doStreamingRequest() helper function always sends multiple requests to the server, which means that if the server already rejects the first message it can be that it will cancel the stream before we have succeeded to send the second request.

Fix this by refactoring doStreamingRequest() to receive an arbitrary number of requests as input. Like this, the tests for invalid requests can only send a single request that will fail validation, while other tests can continue to stress our ability to reassemble the object map.