Fix map vote revert, add admin verb (#89505)

## About The Pull Request

Fixes revert_next_map() not actually reverting the map vote. Also added
an admin verb for it for ease of access.

## Why It's Good For The Game

Fix bug, revert map vote without having to poke around in the subsystem.

## Changelog

🆑 LT3
fix: Revert next map command actually reverts the map vote
admin: Admins now have a verb to revert the map vote
/🆑

code/modules/admin/verbs/maprotation.dm

@@ -114,3 +114,6 @@ ADMIN_VERB(admin_change_map, R_SERVER, "Change Map", "Set the next map.", ADMIN_
 		if (SSmap_vote.set_next_map(virtual_map))
 			message_admins("[key_name_admin(user)] has changed the map to [virtual_map.map_name]")
 			SSmap_vote.admin_override = TRUE
+
+ADMIN_VERB(admin_revert_map, R_SERVER, "Revert Map Vote", "Revert the map vote, allowing a new vote.", ADMIN_CATEGORY_SERVER)
+	SSmap_vote.revert_next_map(user)