[xdg-desktop-portal-gnome] ci: Allow Ubuntu to fail

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit e84a530fa66cf0a0613c159f74fde11cb366f0e7
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed Nov 10 15:03:53 2021 -0300

    ci: Allow Ubuntu to fail
    
    It doesn't ship a recent enough Meson version

 .gitlab-ci.yml | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 4917979..fc38912 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -20,6 +20,7 @@ build-fedora:
 build-ubuntu:
   image: ubuntu:rolling
   extends: .build-common
+  allow_failure: true
   variables:
     DEBIAN_FRONTEND: noninteractive
   before_script: