Test using Git 2.21

Given Rails doesn't use the Git binary anymore, this shouldn't be a
problem.

.gitlab-ci.yml

-image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-golang-1.11-git-2.18-chrome-71.0-node-10.x-yarn-1.12-postgresql-9.6-graphicsmagick-1.3.29"
+image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-golang-1.11-git-2.21-chrome-71.0-node-10.x-yarn-1.12-postgresql-9.6-graphicsmagick-1.3.29"
 variables:
   MYSQL_ALLOW_EMPTY_PASSWORD: "1"

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

@@ -16,7 +16,7 @@
 gitlab:assets:compile:
   <<: *assets-compile-cache
   extends: .dedicated-no-docs-pull-cache-job
-  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-git-2.18-chrome-71.0-node-8.x-yarn-1.12-graphicsmagick-1.3.29-docker-18.06.1
+  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-git-2.21-chrome-71.0-node-8.x-yarn-1.12-graphicsmagick-1.3.29-docker-18.06.1
   dependencies:
     - setup-test-env
   services:
@@ -234,4 +234,4 @@ jsdoc:
     name: jsdoc
     expire_in: 31d
     paths:
-      - jsdoc/
\ No newline at end of file
+      - jsdoc/

.gitlab/ci/rails.gitlab-ci.yml

@@ -86,7 +86,7 @@
 .rspec-metadata-pg-10: &rspec-metadata-pg-10
   <<: *rspec-metadata
   <<: *use-pg-10
-  image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-golang-1.11-git-2.18-chrome-71.0-node-10.x-yarn-1.12-postgresql-10-graphicsmagick-1.3.29"
+  image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-golang-1.11-git-2.21-chrome-71.0-node-10.x-yarn-1.12-postgresql-10-graphicsmagick-1.3.29"
 .rspec-metadata-mysql: &rspec-metadata-mysql
   <<: *rspec-metadata

changelogs/unreleased/zj-git-2-21-tests.yml

+---
+title: Test using Git 2.21
+merge_request: 27418
+author:
+type: added