Merge branch 'update_project_flash_error_message' into 'master'

Set flash error message only for current request when updating project

Closes #43772

See merge request gitlab-org/gitlab-ce!20126

app/controllers/projects_controller.rb

@@ -63,7 +63,7 @@ class ProjectsController < Projects::ApplicationController
           redirect_to(edit_project_path(@project))
         end
       else
-        flash[:alert] = result[:message]
+        flash.now[:alert] = result[:message]
 
         format.html { render 'edit' }
       end

spec/controllers/projects_controller_spec.rb

@@ -329,7 +329,7 @@ describe ProjectsController do
           expect { update_project path: 'renamed_path' }
             .not_to change { project.reload.path }
 
-          expect(controller).to set_flash[:alert].to(/container registry tags/)
+          expect(controller).to set_flash.now[:alert].to(/container registry tags/)
           expect(response).to have_gitlab_http_status(200)
         end
       end