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

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 1addc21f32c57f2e8c4f2203201df92917f5a5c7
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu Aug 20 18:14:28 2020 +0300

    ci: use ubuntu 20.04 image

 .gitlab-ci.yml | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8a881ab..3e1b9e9 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -8,7 +8,7 @@ variables:
   GIT_SUBMODULE_STRATEGY: normal
 
 validate-menu:
-  image: ubuntu:devel
+  image: ubuntu:focal
   stage: validate
   except:
     - tags
@@ -21,7 +21,7 @@ validate-menu:
       data/menus/gnome-flashback-applications.menu
 
 build-ubuntu:
-  image: ubuntu:devel
+  image: ubuntu:focal
   stage: build
   except:
     - tags
@@ -70,7 +70,7 @@ build-ubuntu:
     - make distcheck
 
 coverity:
-  image: ubuntu:devel
+  image: ubuntu:focal
   stage: analysis
   when: manual
   before_script: