Fixes Acid Ball hurting friendly xenos (and self) (#6129)

# About the pull request
As title fixes an oversight causing friendly fire.

# Explain why it's good for the game

FF bad for xenos.


# Testing Photographs and Procedure
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<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
fix: Fixes praetorian acid ball harming the prae and other xenos.
/:cl:

code/datums/ammo/xeno.dm

@@ -186,7 +186,7 @@
 /datum/ammo/xeno/acid/prae_nade // Used by base prae's acid nade
 	name = "acid scatter"
 
-	flags_ammo_behavior = AMMO_STOPPED_BY_COVER
+	flags_ammo_behavior = AMMO_ACIDIC|AMMO_XENO|AMMO_STOPPED_BY_COVER
 	accuracy = HIT_ACCURACY_TIER_5
 	accurate_range = 32
 	max_range = 4