Allow Skittish to Intercept Bump (#96890)

## About The Pull Request

resolves: https://github.com/tgstation/tgstation/issues/56396

Modifies `atoms_movable.dm` and `skittish.md`, as a subscriber to the
`COMSIG_MOVABLE_BUMP` signal, to allow the latter to bubble up an
intercept flag to `living.dm`, so that it can cancel a shove and
function properly.

I looked at every other registered `COMSIG_MOVABLE_BUMP` signal receiver
and found that only one ever possibly returns non-zero, and that is
`/obj/item/clothing/gloves/gauntlets/proc/rocksmash`. However, when
`rocksmash` is called via a bump signal, it will return `NONE` because
the `proximity` parameter will not be set. Therefore, unless I missed
something, there should be no collateral damage from this change.
## Why It's Good For The Game

Skittish has been broken seemingly since its addition to the game. This
fixes that.

<img width="640" height="480" alt="crate"
src="https://github.com/user-attachments/assets/0ce01c07-0e44-498b-aac0-02c448a6d379"
/>
<img width="640" height="480" alt="locker"
src="https://github.com/user-attachments/assets/6fc946fb-e953-43d0-9bd3-9d958a3d9744"
/>

## Changelog
🆑
fix: Fixed Skittish behaving strangely with lockers not against a wall,
and crates in general.
/🆑

code/datums/elements/skittish.dm

@@ -59,3 +59,5 @@
 	closet_turf.visible_message(span_warning("[scooby] dives into [closet]!"))
 	// If you run into a locker, you don't want to run out immediately
 	scooby.Immobilize(0.5 SECONDS)
+
+	return COMPONENT_INTERCEPT_BUMPED