The Gogs developers got it into their head that trying to write things
to some relative path from the binary location is a sensible thing to
do (spoiler: it's not).
Due to their weird "GOGS_CUSTOM" directory which seems to only
sometimes be configurable by environment variables, the command used
to handle SSH requests failed because it attempted to write logs into
the Nix store.
This works around the issue by hardcoding the log file root path in
the Gogs configuration.
