Respect `ref` when searching for commits

Fixes a bug where the branch is always assumed to be
master, even when the user specifies a branch they
want to search

changelogs/unreleased/199245-search-api-seems-to-ignore-ref-returns-spurious-results-from-maste.yml

+---
+title: Fix incorrect commit search results returned when searching with ref
+merge_request: 33216
+author:
+type: fixed

lib/gitlab/project_search_results.rb

@@ -159,7 +159,7 @@ module Gitlab
     end
 
     def find_commits_by_message(query, limit:)
-      project.repository.find_commits_by_message(query, nil, nil, limit)
+      project.repository.find_commits_by_message(query, repository_project_ref, nil, limit)
     end
 
     def find_commit_by_sha(query)

spec/lib/gitlab/project_search_results_spec.rb

@@ -530,6 +530,18 @@ describe Gitlab::ProjectSearchResults do
         expect(commits).to be_empty
       end
 
+      context 'when repository_ref is provided' do
+        let(:message) { 'Feature added' }
+        let(:repository_ref) { +'feature' }
+
+        it 'searches in the specified ref' do
+          commits = described_class.new(user, project, message, repository_ref).objects('commits')
+
+          # This commit is unique to the feature branch
+          expect(commits).to contain_exactly(project.repository.commit('0b4bc9a49b562e85de7cc9e834518ea6828729b9'))
+        end
+      end
+
       it_behaves_like 'access restricted commits' do
         let(:search_phrase) { message }
         let(:commit) { project.repository.commit('59e29889be61e6e0e5e223bfa9ac2721d31605b8') }