(Hopefully) Lessens preferences and manifest injection lag (#30596)

* first step to fixing a potential problem is identifying it

* woops

* kk

* mso is already doing this kek

* yeah lets do that too.

* replicated code

* wups

* wups

* better

* gibe the merge b0ss

* cyberboss

* Update dummy.dm

code/datums/datacore.dm

@@ -196,6 +196,7 @@
 
 
 /datum/datacore/proc/manifest_inject(mob/living/carbon/human/H, client/C)
+	set waitfor = FALSE
 	if(H.mind && (H.mind.assigned_role != H.mind.special_role))
 		var/assignment
 		if(H.mind.assigned_role)
@@ -284,4 +285,4 @@
 		C = H.client
 	if(C)
 		P = C.prefs
-	return get_flat_human_icon(null, J, P)
+	return get_flat_human_icon(null, J, P, DUMMY_HUMAN_SLOT_MANIFEST)