Fix return codes for getting an inexisting release

Updates the returned status codes for getting a release by tag name when
it does not exists.

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/216342

Changelog: fixed

lib/api/releases.rb

@@ -60,6 +60,8 @@ module API
                                desc: 'If `true`, a response includes HTML rendered markdown of the release description.'
       end
       get ':id/releases/:tag_name', requirements: RELEASE_ENDPOINT_REQUIREMENTS do
+        not_found! unless release
+
         authorize_download_code!
 
         present release, with: Entities::Release, current_user: current_user, include_html_description: params[:include_html_description]

spec/requests/api/releases_spec.rb

@@ -463,10 +463,23 @@ RSpec.describe API::Releases do
     end
 
     context 'when specified tag is not found in the project' do
-      it 'cannot find the release entry' do
+      it 'returns 404 for maintater' do
         get api("/projects/#{project.id}/releases/non_exist_tag", maintainer)
 
-        expect(response).to have_gitlab_http_status(:forbidden)
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+
+      it 'returns project not found for no user' do
+        get api("/projects/#{project.id}/releases/non_exist_tag", nil)
+
+        expect(response).to have_gitlab_http_status(:not_found)
+        expect(json_response['message']).to eq('404 Project Not Found')
+      end
+
+      it 'returns 404 for guest' do
+        get api("/projects/#{project.id}/releases/non_exist_tag", guest)
+
+        expect(response).to have_gitlab_http_status(:not_found)
       end
     end