theme: Require GTK 3.24.20 to compile the stylesheet

Let's require a more up-to-date version. This didn't change the
compiled stylesheets.
12 jobs for gtk-3-24-20 in 24 minutes and 45 seconds (queued for 2 minutes and 17 seconds)
Status Job ID Name Coverage
  Build
passed #266985
librem5
api-visibility

00:02:54

passed #266987
librem5
build-debian-clang

00:04:43

passed #266986
librem5
build-debian-gcc

00:03:20

passed #266988
librem5
build-fedora-gcc

00:03:25

 
  Test+Docs
passed #266989
librem5
build-gtkdoc

00:03:03

passed #266990
librem5
unit-test

00:03:03

41.1%
 
  Package
passed #266991
librem5
package-debian-buster

00:03:30

passed #266992
librem5:arm64
package-debian-buster:arm64

00:06:14

failed #266993
flatpak allowed to fail
package-flatpak

00:00:19

failed #266994
flatpak allowed to fail
package-flatpak-glade

00:00:23

 
  Test Package
passed #266995
librem5
autopkgtest-debian-buster-package

00:03:05

passed #266996
librem5
lintian-debian-buster-package

00:01:10

 
Name Stage Failure
failed
package-flatpak-glade Package
rm: Running after_script
cannot remove '_build/src/25a6634@@handy-1@sha/hdy-application-window.c.gcda': Permission denied
rm: cannot remove '_build/src/25a6634@@handy-1@sha/hdy-preferences-page.c.o': Permission denied
rm:
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=266994 responseStatus=201 Created token=z1V6JSfm
ERROR: Job failed: exit code 1
failed
package-flatpak Package
rm: cannot remove '_build/meson-logs/coveragereport/builds/adrien.plazas/libhandy/src/hdy-keypad.h.func.html': Permission denied
rm: cannot remove '_build/meson-logs/coveragereport/builds/adrien.plazas/libhandy/src/hdy-search-bar.h.gcov.html': Permission denied
rm: cannot remove '_build/meson-logs/coveragereport/builds/adrien.plazas/libhandy/src/hdy-swipeable.c.func-sort-c.html': Permission denied
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=266993 responseStatus=201 Created token=C17d_ZhJ
ERROR: Job failed: exit code 1