[MIRROR] Anchors mapping helpers so they don't get put inside crates [MDB IGNORE] (#21117)

* Anchors mapping helpers so they don't get put inside crates (#75387)

## About The Pull Request

Persistent Birdshot CI failure was caused by broken floor helper sharing
a tile with a random loot spawner, which would sometimes spawn a
maintenance crate which deletes itself, but only after the crate eats
the mapping helper. This causes the mapping helper to delete before it
has initialised.

There's no reason for a mapper to assume this would cause a problem so
the fix isn't to edit the map, instead I just anchored all mapping
helpers so that closets won't try to contain them.

## Why It's Good For The Game

I'm really tired of birdshot failing CI
This probably fixes some other really niche bug nobody has noticed

## Changelog

Not player facing

* Anchors mapping helpers so they don't get put inside crates

---------

Co-authored-by: Jacquerel <hnevard@gmail.com>

code/modules/mapping/mapping_helpers.dm

@@ -103,6 +103,7 @@
 /obj/effect/mapping_helpers
 	icon = 'icons/effects/mapping_helpers.dmi'
 	icon_state = ""
+	anchored = TRUE
 	var/late = FALSE
 
 /obj/effect/mapping_helpers/Initialize(mapload)