[gnome-shell] ci: Update mutter image

[Marge Bot <marge-bot src gnome org>]

commit e81cab540f868c76d82bbcf7867d1182620f7971
Author: Florian Müllner <fmuellner gnome org>
Date:   Fri Nov 20 15:56:01 2020 +0100

    ci: Update mutter image
    
    Mutter now produces an image as part of its CI pipeline. Use that
    instead of the now outdated manually built image.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1504>

 .gitlab-ci.yml | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 3af90bca80..ae82170c2a 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -15,6 +15,8 @@ variables:
     LINT_LOG: "eslint-report.xml"
     LINT_MR_LOG: "eslint-mr-report.xml"
 
+image: registry.gitlab.gnome.org/gnome/mutter/fedora/33:2020-11-20.1
+
 .only_default: &only_default
     only:
         - branches
@@ -57,7 +59,6 @@ build-fedora-container:
     <<: *only_default
 
 check_commit_log:
-    image: registry.gitlab.gnome.org/gnome/mutter/master:v4
     stage: review
     variables:
         GIT_DEPTH: "100"
@@ -135,7 +136,6 @@ no_template_check:
     <<: *only_default
 
 build:
-    image: registry.gitlab.gnome.org/gnome/mutter/master:v4
     stage: build
     needs: ["check_commit_log"]
     before_script:
@@ -154,7 +154,6 @@ build:
             - build
 
 test:
-    image: registry.gitlab.gnome.org/gnome/mutter/master:v4
     stage: test
     needs: ["build"]
     variables: