MM-29486: Fix racy test TestPatchChannelModeration (#16256)

* MM-29486: Fix racy test TestPatchChannelModeration

- We avoid appending to the slice in `(r *Role) IsValidWithoutId`
by just iterating the 2 slices separately.
- We pass deep copies of channels to prevent racy modification.

https://mattermost.atlassian.net/browse/MM-29486

```release-note
NONE
```

* fix lint

* simplify perm check

* improve more

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/channel_test.go

@@ -1828,15 +1828,15 @@ func TestPatchChannelModerationsForChannel(t *testing.T) {
 		wg.Add(20)
 		for i := 0; i < 10; i++ {
 			go func() {
-				th.App.PatchChannelModerationsForChannel(channel, addCreatePosts)
-				th.App.PatchChannelModerationsForChannel(channel, removeCreatePosts)
+				th.App.PatchChannelModerationsForChannel(channel.DeepCopy(), addCreatePosts)
+				th.App.PatchChannelModerationsForChannel(channel.DeepCopy(), removeCreatePosts)
 				wg.Done()
 			}()
 		}
 		for i := 0; i < 10; i++ {
 			go func() {
-				th.App.PatchChannelModerationsForChannel(channel, addCreatePosts)
-				th.App.PatchChannelModerationsForChannel(channel, removeCreatePosts)
+				th.App.PatchChannelModerationsForChannel(channel.DeepCopy(), addCreatePosts)
+				th.App.PatchChannelModerationsForChannel(channel.DeepCopy(), removeCreatePosts)
 				wg.Done()
 			}()
 		}