theme: Require preferencesgroup instead of window for h4

HdyPreferencesGroup has a label with h4 style class, which is supposed to
be bold. However, it's only bold when the group is also inside a
HdyPreferencesWindow, which doesn't make much sense. So instead style h4
labels instead of preferences groups instead of windows.
12 jobs for wip/exalm/h4 in 14 minutes and 42 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #267485
librem5
api-visibility

00:02:54

passed #267487
librem5
build-debian-clang

00:04:18

passed #267486
librem5
build-debian-gcc

00:03:20

passed #267488
librem5
build-fedora-gcc

00:03:57

 
  Test+Docs
passed #267489
librem5
build-gtkdoc

00:02:10

passed #267490
librem5
unit-test

00:02:05

41.1%
 
  Package
passed #267491
librem5
package-debian-buster

00:02:05

passed #267492
librem5:arm64
package-debian-buster:arm64

00:06:09

failed #267493
flatpak allowed to fail
package-flatpak

00:02:17

failed #267494
flatpak allowed to fail
package-flatpak-glade

00:00:15

 
  Test Package
passed #267495
librem5
autopkgtest-debian-buster-package

00:02:03

passed #267496
librem5
lintian-debian-buster-package

00:00:49

 
Name Stage Failure
failed
package-flatpak-glade Package
rm: cannot remove '_build/tests/test-header-group': Permission denied
rm: cannot remove '_build/tests/59830eb@@test-application-window@exe/test-application-window.c.o': Permission denied
rm: cannot remove '_build/tests/59830eb@@test-application-window@exe/test-application-window.c.gcno': Permission denied
Uploading artifacts for failed job
Uploading artifacts...
_build/meson-logs/meson-log.txt: found 1 matching files

WARNING: sm.puri.Handy.Glade-dev.flatpak: no matching files
Uploading artifacts to coordinator... ok
id=267494 responseStatus=201 Created token=yj54Xy8M
ERROR: Job failed: exit code 1
failed
package-flatpak Package
rm: cannot remove '_build/src/25a6634@@handy-1@sha/hdy-leaflet.c.gcda': Permission denied
rm: cannot remove '_build/src/25a6634@@handy-1@sha/hdy-header-group.c.gcda': Permission denied
rm: cannot remove '_build/src/25a6634@@handy-1@sha/hdy-navigation-direction.c.
Running after_script
Uploading artifacts for failed job
Uploading artifacts...
_build/meson-logs/meson-log.txt: found 1 matching files

WARNING: sm.puri.Handy.Demo-dev.flatpak: no matching files
Uploading artifacts to coordinator... ok
id=267493 responseStatus=201 Created token=7A7Ssz3u
ERROR: Job failed: exit code 1