[libnotify: 1/2] fix CI build stuck on TZ data config

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 698a05fcc49e40c6b6f2990a5e1205cd5f93d028
Author: Matthias Sweertvaegher <46206-matthias sweertvaegher users noreply gitlab gnome org>
Date:   Mon Dec 14 17:44:11 2020 +0100

    fix CI build stuck on TZ data config
    
    when pushing a new commit, I noticed the CI build gets stuck on:
    
    Configuring tzdata
    ------------------
    Please select the geographic area in which you live. Subsequent configuration
    questions will narrow this down by presenting a list of cities, representing
    the time zones in which they are located.
      1. Africa   3. Antarctica  5. Arctic  7. Atlantic  9. Indian    11. US
      2. America  4. Australia   6. Asia    8. Europe    10. Pacific  12. Etc
    Geographic area:

 .gitlab-ci.yml | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 0730092..7dd1840 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,3 +1,6 @@
+variables:
+  DEBIAN_FRONTEND: noninteractive
+
 stages:
   - build