ci: Allow failure of the build_deb-CI-job

Some of the build-dependencies that were installed from Debian Unstable
as a workaround, are not available anymore.

Until that issue has been solved properly, allow the `build_deb`-CI-job
to fail, so that merge-requests can still be merged.

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/653>

.gitlab-ci.yml

@@ -56,6 +56,7 @@ build_meson:
       - $PKG_ONLY == "1"
 
 build_deb:
+  allow_failure: true
   tags:
     - aarch64
   stage: build
@@ -64,18 +65,19 @@ build_deb:
       - '*.deb'
   script:
     - rm -f ../*.deb
-    - apt-get -y build-dep .
-    - apt-get -y install devscripts
 # Workaround for unavailable dependencies
 # TODO: Port Squeekboard to GTK4/GTK4-layer-shell
 # https://gitlab.gnome.org/World/Phosh/squeekboard/-/issues/64
     - echo "deb http://deb.debian.org/debian/ unstable main" > /etc/apt/sources.list.d/unstable.list
     - echo "deb http://deb.debian.org/debian/ experimental main" > /etc/apt/sources.list.d/experimental.list
+    - echo "APT::Default-Release \"trixie\";" > /etc/apt/apt.conf.d/default-release
     - apt-get -y update
     - apt-get -y --no-upgrade install librust-gio-dev librust-glib-dev librust-glib-sys-dev
       librust-gtk-dev librust-gtk-sys-dev
     - apt-get -y --no-upgrade install -t experimental librust-serde-yaml-dev
 # End of workaround for unavailable dependencies
+    - apt-get -y build-dep .
+    - apt-get -y install devscripts
     - REV=$(git log -1 --format=%h)
     - VER=$(dpkg-parsechangelog -SVersion)
     - DEBFULLNAME="Librem5 CI"