`GracefulShutdownManager` is likely not working as expected

[peppy]

The original goal was to wait for all gameplay and multiplayer sessions to finish, but checking on staging the server was failing to shut down with this state:

Seems like something has regressed here

[smoogipoo]

ConnectionState seems to be the concurrent connection limiter. This particular change appears to have been done intentionally in 54226e7, so cc/ @bdach

[bdach]

I'll look into it, but it seems weird that this surfaced after more than a year if it is that change.

[peppy]

We've seen it waiting for 6 hours every shutdown for a long while but it's never really been a blocker, just a "hmm".

I open this because I managed to reproduce on staging with likely one user connected and idle. Should be pretty easy to repro if that's the case.