[metacity/test] ci: use ubuntu 21.04 image

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 3e4080cbee7e32d338518c80c5b1e5c20a8391b3
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu May 13 19:49:21 2021 +0300

    ci: use ubuntu 21.04 image

 .gitlab-ci.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 7a967c5b..5518548b 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -39,7 +39,7 @@ variables:
                   zenity
 
 ubuntu:
-  image: ubuntu:devel
+  image: ubuntu:hirsute
   stage: build
   except:
     - tags
@@ -52,7 +52,7 @@ ubuntu:
     - make distcheck
 
 coverity:
-  image: ubuntu:devel
+  image: ubuntu:hirsute
   stage: analysis
   when: manual
   before_script: