Fix `ruff server` hanging after Neovim closes (#11291)
## Summary
A follow-up to https://github.com/astral-sh/ruff/pull/11222. `ruff
server` stalls during shutdown with Neovim because after it receives an
exit notification and closes the I/O thread, it attempts to log a
success message to `stderr`. Removing this log statement fixes this
issue.
## Test Plan
Track the instances of `ruff` in the OS task manager as you open and
close Neovim. A new instance should appear when Neovim starts and it
should disappear once Neovim is closed.
