Remove hardcoded default branch name from FE tests

spec/frontend/blob/viewer/index_spec.js

@@ -28,7 +28,7 @@ describe('Blob viewer', () => {
     loadFixtures('blob/show_readme.html');
     $('#modal-upload-blob').remove();
 
-    mock.onGet(/blob\/master\/README\.md/).reply(200, {
+    mock.onGet(/blob\/.+\/README\.md/).reply(200, {
       html: '<div>testing</div>',
     });
 

spec/frontend/fixtures/blob.rb

@@ -34,7 +34,7 @@ RSpec.describe Projects::BlobController, '(JavaScript fixtures)', type: :control
     get(:show, params: {
       namespace_id: project.namespace,
       project_id: project,
-      id: 'master/README.md'
+      id: "#{project.default_branch}/README.md"
     })
 
     expect(response).to be_successful