repository: Add tests for F/D conflicts in FetchRemote
When fetching refs from a source, there is a potential F/D conflict which can occur. Consider the following:
- Source => {refs: ["refs/heads/branch": commit1]}
- Mirror => {refs: ["refs/heads/branch/conflict": commit2]}
When we pull the refs from the source to the mirror, there is potential scenario where there is a F/D conflict.
In FetchRemote we prune refs before fetching, unless NoPrune option is specified. Because of this, there is no F/D conflict occuring by default.
Add tests to validate this behavior and codify it.
Part of #4389 (closed)