region: Autodisconnect IBusBus "connected" handler

Use g_signal_connect_object to ensure handler is not run after object is
destroyed.

Fixes: GNOME/gnome-control-center#223
11 jobs for fix-issue-223-3-30 in 4 minutes and 21 seconds (queued for 1 minute and 14 seconds)
latest
Status Job ID Name Coverage
  Build
passed #142041
build

00:01:58

 
  Test
passed #142043
asan

00:01:40

passed #142042
test

00:00:42

 
  Manual
manual #142048
allowed to fail manual
armv8
manual #142044
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flatpak
manual #142047
allowed to fail manual
msan
manual #142049
allowed to fail manual
ppc64le
manual #142045
allowed to fail manual
tsan
manual #142046
allowed to fail manual
ubsan
 
  Review
manual #142050
allowed to fail manual
review
manual #142051
allowed to fail manual
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