power: Don't use gtk_widget_show_all

It is removed in GTK+ 4
11 jobs for power-no-no-show-all in 4 minutes and 27 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #122799
build

00:01:43

 
  Test
passed #122801
asan

00:02:11

passed #122800
test

00:00:40

 
  Manual
manual #122806
allowed to fail manual
armv8
manual #122802
allowed to fail manual
flatpak
manual #122805
allowed to fail manual
msan
manual #122807
allowed to fail manual
ppc64le
manual #122803
allowed to fail manual
tsan
manual #122804
allowed to fail manual
ubsan
 
  Review
manual #122808
allowed to fail manual
review
manual #122809
allowed to fail manual
stop_review