Update CI build image to use yarn 1.21

.gitlab-ci.yml

-image: "registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.16-postgresql-9.6-graphicsmagick-1.3.34"
+image: "registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.21-postgresql-9.6-graphicsmagick-1.3.34"
 
 stages:
   - sync

.gitlab/ci/frontend.gitlab-ci.yml

@@ -78,7 +78,7 @@
     - .default-retry
     - .default-before_script
     - .assets-compile-cache
-  image: registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.16-graphicsmagick-1.3.34-docker-19.03.1
+  image: registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.21-graphicsmagick-1.3.34-docker-19.03.1
   stage: prepare
   services:
     - docker:19.03.0-dind

.gitlab/ci/global.gitlab-ci.yml

@@ -203,7 +203,7 @@
     - name: redis:alpine
 
 .use-pg10:
-  image: "registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.16-postgresql-10-graphicsmagick-1.3.34"
+  image: "registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.21-postgresql-10-graphicsmagick-1.3.34"
   services:
     - name: postgres:10.9
       command: ["postgres", "-c", "fsync=off", "-c", "synchronous_commit=off", "-c", "full_page_writes=off"]
@@ -217,7 +217,7 @@
     - name: elasticsearch:6.4.2
 
 .use-pg10-ee:
-  image: "registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.16-postgresql-10-graphicsmagick-1.3.34"
+  image: "registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.21-postgresql-10-graphicsmagick-1.3.34"
   services:
     - name: postgres:10.9
       command: ["postgres", "-c", "fsync=off", "-c", "synchronous_commit=off", "-c", "full_page_writes=off"]

doc/development/pipelines.md

@@ -42,9 +42,9 @@ The current stages are:
 ## Default image
 
 The default image is currently
-`registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.16-postgresql-9.6-graphicsmagick-1.3.34`.
+`registry.gitlab.com/gitlab-org/gitlab-build-images:ruby-2.6.5-golang-1.12-git-2.24-lfs-2.9-chrome-73.0-node-12.x-yarn-1.21-postgresql-9.6-graphicsmagick-1.3.34`.
 
-It includes Ruby 2.6.5, Go 1.12, Git 2.24, Git LFS 2.9, Chrome 73, Node 12, Yarn 1.16,
+It includes Ruby 2.6.5, Go 1.12, Git 2.24, Git LFS 2.9, Chrome 73, Node 12, Yarn 1.21,
 PostgreSQL 9.6, and Graphics Magick 1.3.33.
 
 The images used in our pipelines are configured in the