:beetle: Fix thunderbird auto-assigned workspace

Class name changed after Thunderbird update.

Unfortunately, class name "Mail" is not working, still have to use
"thunderbird" (but without caps to fix the issue).

Install/Templates/home/config/regolith/i3/config

@@ -488,7 +488,7 @@ for_window [class="Mumble"] move scratchpad
 
 # Auto set workspaces
 for_window [class="^Gimp.*"] move container to workspace $ws15
-for_window [class="Thunderbird"] move container to workspace $ws6
+for_window [class="thunderbird"] move container to workspace $ws6
 
 ###############################################################################
 # Window Resize and Gaps