ci: Build our own gtk3 containing unreleased bug fix

Contains https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/7139 which
is needed for test suite improvements.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3700>

.gitlab-ci.yml

@@ -85,7 +85,7 @@ variables:
     - .skip-git-clone
   variables:
     FDO_DISTRIBUTION_VERSION: 40
-    BASE_TAG: '2024-04-29.0'
+    BASE_TAG: '2024-05-02.0'
     MUTTER_USER: 'meta-user'
     FDO_DISTRIBUTION_PACKAGES:
       asciidoc
@@ -131,7 +131,13 @@ variables:
 
       rpm -e --nodeps gnome-bluetooth-libs-devel \
                       mutter mutter-devel \
-                      gnome-shell
+                      gnome-shell \
+                      gtk3
+
+      # Contains fixes needed for tests not included in 3.24.33
+      ./.gitlab-ci/install-meson-project.sh \
+        https://gitlab.gnome.org/GNOME/gtk.git \
+        gtk-3-24 46fe3224dd771b91e6976d5a632b452e2179a4f0
 
       # Work-around for podman-push aborting on permission issue
       # https://gitlab.gnome.org/Infrastructure/Infrastructure/-/issues/1247