[gnome-panel/gnome-3-36] ci: use ubuntu 20.04 image

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 39a427ed15cf645b14419c7eaa6c370e0914c8d0
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Wed Aug 26 17:52:19 2020 +0300

    ci: use ubuntu 20.04 image

 .gitlab-ci.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 14face0ff..3fde8e43e 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -6,7 +6,7 @@ variables:
   DEBIAN_FRONTEND: noninteractive
 
 build-ubuntu:
-  image: ubuntu:devel
+  image: ubuntu:focal
   stage: build
   except:
     - tags
@@ -50,7 +50,7 @@ build-ubuntu:
     - make distcheck
 
 coverity:
-  image: ubuntu:devel
+  image: ubuntu:focal
   stage: analysis
   when: manual
   before_script: