gid mismatch between entrypoint and dockerfile

In #96, the uid and gid were changed to 1092 with user name `taskchampion`. Then in #99, the gid in the entrypoint was changed from 1092 to `users`, but this only affects the `data` subdirectory. In fact, if you check on a running image, you will see both gids:
```
$ podman exec -it systemd-taskchampion /bin/sh
/ # ls -l /var/lib/
total 0
drwxr-xr-x 2 root root 0 Oct 8 09:31 misc
drwxr-xr-t 3 taskcham 1092 8 Jan 10 10:31 taskchampion-sync-server
/ # ls -l /var/lib/taskchampion-sync-server/
total 4
drwx------ 1 taskcham users 64 Jan 10 10:31 data
```
i.e., `/var/lib/taskchampion-sync-server` is 1092:1092, but `/var/lib/taskchampion-sync-server/data` is 1092:100.

Note, the actual name doesn't matter, only the numeric ID is recorded on the file system, and the name is just for display purposes. It is a bit confusing to see both though and would be good to make them consistent.

As I'm using rootless podman, I'm not sure if reverting back to gid 100 is problematic for #87, or if only the uid 100 is a problem.