Fix TestUserMergeBranch_abort flaking due to a timeout
TestUserMergeBranch_abort sets a one second timeout for receiving a response from stream. This is not needed as the test is not testing the timeout behavior. As this is causing flakes on slower runners, let's remove the timeout.
Fixes https://gitlab.com/gitlab-org/gitaly/-/jobs/3407227173
Edited by Sami Hiltunen