Merge branch 'zj-branch-containing-sha-opt-out' into 'master'

Branch with a commit detection defaults to Gitaly

See merge request gitlab-org/gitlab-ce!18304

changelogs/unreleased/zj-branch-containing-sha-opt-out.yml

+---
+title: Detecting branchnames containing a commit uses Gitaly by default
+merge_request:
+author:
+type: performance

lib/gitlab/git/repository.rb

@@ -1385,7 +1385,8 @@ module Gitlab
       end
       def branch_names_contains_sha(sha)
-        gitaly_migrate(:branch_names_contains_sha) do |is_enabled|
+        gitaly_migrate(:branch_names_contains_sha,
+                      status: Gitlab::GitalyClient::MigrationStatus::OPT_OUT) do |is_enabled|
           if is_enabled
             gitaly_ref_client.branch_names_contains_sha(sha)
           else