Allows M46C to take rubber munitions (cmss13-devs#4541)

# About the pull request

<!-- Remove this text and explain what the purpose of your PR is.

Mention if you have tested your changes. If you changed a map, make sure
you used the mapmerge tool.
If this is an Issue Correction, you can type "Fixes Issue #169420" to
link the PR to the corresponding Issue number #169420.

Remember: something that is self-evident to you might not be to others.
Explain your rationale fully, even if you feel it goes without saying.
-->

Allows M46C to take rubber munitions
# Explain why it's good for the game
bug bad 
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

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

</details>


# Changelog
:cl:
fix: Allows M46C prototype rifle to accept standard M41A MK2 rubber
munitions
/:cl:

code/modules/projectiles/guns/rifles.dm

@@ -435,6 +435,7 @@
 
 	accepted_ammo = list(
 		/obj/item/ammo_magazine/rifle,
+		/obj/item/ammo_magazine/rifle/rubber,
 		/obj/item/ammo_magazine/rifle/extended,
 		/obj/item/ammo_magazine/rifle/ap,
 		/obj/item/ammo_magazine/rifle/incendiary,