fix 404 error, redirect back with flash message

app/controllers/import/gitlab_projects_controller.rb

@@ -27,10 +27,7 @@ class Import::GitlabProjectsController < Import::BaseController
         notice: "Project '#{@project.name}' is being imported."
       )
     else
-      redirect_to(
-        new_import_gitlab_project_path,
-        alert: "Project could not be imported: #{@project.errors.full_messages.join(', ')}"
-      )
+      redirect_back_or_default(options: { alert: "Project could not be imported: #{@project.errors.full_messages.join(', ')}" })
     end
   end