Merge branch 'ci_default_git_depth_only' into 'master'

API: Allow changing only ci_default_git_depth

See merge request gitlab-org/gitlab-ce!30888

changelogs/unreleased/ci_default_git_depth_only.yml

+---
+title: 'API: Allow changing only ci_default_git_depth'
+merge_request: 30888
+author: Mathieu Parent
+type: fixed

lib/api/helpers/projects_helpers.rb

@@ -71,6 +71,7 @@ module API
           :build_timeout,
           :builds_access_level,
           :ci_config_path,
+          :ci_default_git_depth,
           :container_registry_enabled,
           :default_branch,
           :description,