- The code that gets contributor stats tried to store an
`map[string]*ContributorData` type in the cache, this works for the
memory cache but not for other caches such as Redis.
- The cache implementation for Redis would convert this map via
`fmt.Sprintf` to an string, which would simply print the pointer and not
the value of the pointer. Storing pointers is a no-go as this will get
GC-ed eventually within a few minutes. Therefore store everything with
json, that does properly store the value of the pointers.
- Adds unit test that verifies JSON is being used.
- Resolves https://codeberg.org/forgejo/forgejo/issues/3158
4c8b67c4b2