MM-52743: Skip racy test Test_SendNotifyAdminPosts (#23360)

https://mattermost.atlassian.net/browse/MM-52743
```release-note
NONE
```

server/channels/app/notify_admin_test.go

@@ -19,7 +19,7 @@ import (
 const PluginIdGithub = "github"
 
 func Test_SendNotifyAdminPosts(t *testing.T) {
-
+	t.Skip("MM-52743")
 	t.Run("no error sending non trial upgrade post when no notifications are available", func(t *testing.T) {
 		th := Setup(t).InitBasic()
 		defer th.TearDown()