API: Fix default branch protection setting for Admin API

changelogs/unreleased/55111-gitlab-api-does-not-manage-default_branch_protection-3-value.yml

+---
+title: 'API: Fix default_branch_protection admin setting'
+merge_request: 24398
+author: Robert Schilling
+type: fixed

lib/api/settings.rb

@@ -35,7 +35,7 @@ module API
       end
       optional :container_registry_token_expire_delay, type: Integer, desc: 'Authorization token duration (minutes)'
       optional :default_artifacts_expire_in, type: String, desc: "Set the default expiration time for each job's artifacts"
-      optional :default_branch_protection, type: Integer, values: [0, 1, 2], desc: 'Determine if developers can push to master'
+      optional :default_branch_protection, type: Integer, values: Gitlab::Access.protection_values, desc: 'Determine if developers can push to master'
       optional :default_group_visibility, type: String, values: Gitlab::VisibilityLevel.string_values, desc: 'The default group visibility'
       optional :default_project_visibility, type: String, values: Gitlab::VisibilityLevel.string_values, desc: 'The default project visibility'
       optional :default_projects_limit, type: Integer, desc: 'The maximum number of personal projects'

spec/requests/api/settings_spec.rb

@@ -63,7 +63,8 @@ describe API::Settings, 'Settings' do
             terms: 'Hello world!',
             performance_bar_allowed_group_path: group.full_path,
             instance_statistics_visibility_private: true,
-            diff_max_patch_bytes: 150_000
+            diff_max_patch_bytes: 150_000,
+            default_branch_protection: Gitlab::Access::PROTECTION_DEV_CAN_MERGE
           }
 
         expect(response).to have_gitlab_http_status(200)
@@ -88,6 +89,7 @@ describe API::Settings, 'Settings' do
         expect(json_response['performance_bar_allowed_group_id']).to eq(group.id)
         expect(json_response['instance_statistics_visibility_private']).to be(true)
         expect(json_response['diff_max_patch_bytes']).to eq(150_000)
+        expect(json_response['default_branch_protection']).to eq(Gitlab::Access::PROTECTION_DEV_CAN_MERGE)
       end
     end