Prevent project team from being truncated too early during project destruction

There are two issues with truncating the project team early:

1. `Projects::UnlinkForkService` may not close merge requests properly since
   permissions may be revoked early.

2. If an error is encountered during flushing of caches, then the user will
   lose all privileges, possibly causing an issue on deletion on retry.

app/services/projects/destroy_service.rb

@@ -17,8 +17,6 @@ module Projects
     def execute
       return false unless can?(current_user, :remove_project, project)
-      project.team.truncate
-
       repo_path = project.path_with_namespace
       wiki_path = repo_path + '.wiki'
@@ -30,6 +28,7 @@ module Projects
       Projects::UnlinkForkService.new(project, current_user).execute
       Project.transaction do
+        project.team.truncate
         project.destroy!
         unless remove_registry_tags

spec/services/projects/destroy_service_spec.rb

@@ -50,6 +50,25 @@ describe Projects::DestroyService, services: true do
     it { expect(Dir.exist?(remove_path)).to be_truthy }
   end
+  context 'when flushing caches fail' do
+    before do
+      new_user = create(:user)
+      project.team.add_user(new_user, Gitlab::Access::DEVELOPER)
+      allow_any_instance_of(Projects::DestroyService).to receive(:flush_caches).and_raise(Redis::CannotConnectError)
+    end
+
+    it 'keeps project team intact upon an error' do
+      Sidekiq::Testing.inline! do
+        begin
+          destroy_project(project, user, {})
+        rescue Redis::CannotConnectError
+        end
+      end
+
+      expect(project.team.members.count).to eq 1
+    end
+  end
+
   context 'with async_execute' do
     let(:async) { true }