Unquarantin rebase test

This test passed on a local execution. Because of this
I am going to unquarantine this test and keep a close
eye on this.

qa/qa/page/merge_request/show.rb

@@ -183,7 +183,11 @@ module QA
         end
 
         def fast_forward_possible?
-          has_no_text?('Fast-forward merge is not possible')
+          has_text?('Fast-forward merge without a merge commit')
+        end
+
+        def fast_forward_not_possible?
+          has_text?('Fast-forward merge is not possible')
         end
 
         def has_file?(file_name)

qa/qa/specs/features/browser_ui/3_create/merge_request/rebase_merge_request_spec.rb

 # frozen_string_literal: true
 
 module QA
-  RSpec.describe 'Create', quarantine: { issue: 'https://gitlab.com/gitlab-org/gitlab/-/issues/30226', type: :bug } do
+  RSpec.describe 'Create', quarantine: { only: { subdomain: :staging }, issue: 'https://gitlab.com/gitlab-org/gitlab/-/issues/323990', type: :flaky } do
     describe 'Merge request rebasing' do
       it 'user rebases source branch of merge request', testcase: 'https://gitlab.com/gitlab-org/quality/testcases/-/issues/1274' do
         Flow::Login.sign_in
@@ -34,7 +34,7 @@ module QA
 
         Page::MergeRequest::Show.perform do |merge_request|
           expect(merge_request).to have_content('Needs rebasing')
-          expect(merge_request).not_to be_fast_forward_possible
+          expect(merge_request).to be_fast_forward_not_possible
           expect(merge_request).not_to have_merge_button
 
           merge_request.rebase!