emulators/citra: unbreak fetch after 66e2037c4970

Failover between mirrors doesn't work if file exists but is different.

> Attempting to fetch https://api.citra-emu.org/gamedb/?dummy=/citra/compatibility_list.json

[...]

> SHA256 Checksum mismatch for citra/compatibility_list.json.

[...]

> Giving up on fetching files: citra/compatibility_list.json

Reported by: pkg-fallout