/mainloop/timeouts test: Reduce race condition

Due to load, particular traits of the architecture, or other circumstances, the
/mainloop/timeouts sometimes manages to call the "every
100 ms" timer loop only 9 times in 1050 ms.

This is an inherent race-condition in the test; allow it some slack and accept
9 times as well.

https://bugzilla.gnome.org/show_bug.cgi?id=678959