feat: inventory full duplicate message fix

[JosTheDude]

This patches a minor visual issue with the error message regarding a full inventory when selling an unsellable item.

What's the issue?
The /sellgui function gives an incorrect error message when attempting to place an unsellable item into the GUI. It says the player’s inventory is full and excess items were dropped on the ground, even when the inventory has plenty of empty space.

Steps to reproduce:

Open /sellgui.
Have empty inventory slots available.
Attempt to place an unsellable item into the sell GUI.
Observe the message:
“Shop > Your inventory is currently full, so excess items have been dropped on the ground.”

Expected result:

The GUI should either:

reject the item with a message stating the item is unsellable, or
return the item normally without claiming the inventory is full.

Actual result:

The system displays an inventory full message and claims items were dropped, even when the player has available inventory space.

What's this PR do?
Patches that! :D

Credit to @Tarmk for the original issue report in our servers' discord

[JosTheDude]

Still prod testing this then will swap to ready for review!

[JosTheDude]

Confirmed & ready for merge - prod tested running latest Folia w/ around 200+ players.

[JosTheDude]

@MackenzieMolloy It looks like some of the PRs here take a bit for visibility, so I'm mentioning as this is a bug patch rather than a feature addition or similar ^-^

[MackenzieMolloy]

This PR looks good however please remove the plugin version bump (1.1.9).

[JosTheDude]

This PR looks good however please remove the plugin version bump (1.1.9).

Done! This was mostly for our reference to indicate we were running the updated version, shouldn't have included that here 🫡