repository: Make `GetSnapshot` backup reftables
The GetSnapshot
RPC is used to backup objects, refs and other important aspects of a git repository. In this sense it also makes sense to backup reftabes as they're introduced.
Let's add the reftable folder to the backup directives and fix the tests to consider reftables too. With this we can also remove the skip we added to the GetSnapshotTest
.
Closes #5840 (closed)