ci: Use debian's gtk package instead of building our own

GTK 4.14 needs a newer glib, but we cannot build and use our own
because the system glib ends up taking precedence because cargo-c
doesn't set RPATHs for the plugins it builds.

The oldest GTK that supports glib 2.74 is GTK 4.10, and Debian 12
ships GTK 4.8, so let's just use the system GTK.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1500>

.gitlab-ci.yml

@@ -142,10 +142,9 @@ trigger:
       libpango1.0-dev libcairo2-dev libjson-glib-dev libgdk-pixbuf-2.0-dev
       libtiff-dev libpng-dev libjpeg-dev libepoxy-dev libsass-dev sassc
       libcsound64-dev llvm clang nasm libsodium-dev libwebp-dev
-      libflac-dev libmysofa-dev
+      libflac-dev libmysofa-dev libgtk-4-dev
-    # glib in bookworm is too old, need 2.76 for gtk-4.14
     FDO_DISTRIBUTION_EXEC: >-
-      bash ci/install-gst.sh --force-fallback-for=glib &&
+      bash ci/install-gst.sh &&
       bash ci/install-dav1d.sh &&
       pip3 install --break-system-packages git+http://gitlab.freedesktop.org/freedesktop/ci-templates
 

ci/install-gst.sh

@@ -30,8 +30,6 @@ meson setup build \
     -Dprefix=/usr/local \
     -Dgpl=enabled \
     -Dugly=enabled \
-    -Dgtk=enabled \
-    -Dgtk:vulkan=disabled \
     -Dexamples=disabled \
     -Dgtk_doc=disabled \
     -Dintrospection=disabled \