Enable Praefect in various tests
Some tests disable Praefect in them without really needing to do so. The reason may be either slightly diverging behavior between Gitaly or Praefect or just differing error messages. We should rather accommodate for the diverging behavior as disabling Praefect in the tests means the RPC won't necessarily get tested with Praefect at all. This MR enables Praefect in various tests and updates their assertions to accommodate for slight divergences in behavior. Eventually we may want to fix the divergences to ensure Praefect and Gitaly behave the same.