Fix typo in animated grass instructions (#1404)

## Changes

Simply a typo correction (th -> the)

"To add animated grass to th Grass material:" -> "To add animated grass
to the Grass material:"

## Checks

By submitting your pull request for review, you agree to the following:

- [x] This contribution was created in whole or in part by me, and I
have the right to submit it under the terms of this repository's open
source licenses.
- [x] I understand and agree that this contribution and a record of it
are public, maintained indefinitely, and may be redistributed under the
terms of this repository's open source licenses.
- [x] To the best of my knowledge, all proposed changes are accurate.

Co-authored-by: IgnisRBX <[email protected]>

Author: kraftw

content/en-us/parts/terrain.md

@@ -171,7 +171,7 @@ While most materials are static, you can add animated blades of grass to the `En
 Note that the speed of animated grass — but not its vector direction — will be reduced if the player has toggled on the **Reduce Motion** [accessibility](../production/publishing/accessibility.md#reduced-motion) setting from the Roblox or in‑experience **Settings** menu.
 </Alert>
 
-To add animated grass to th `Enum.Material.Grass|Grass` material:
+To add animated grass to the `Enum.Material.Grass|Grass` material:
 
 1. In the **Explorer** window, navigate to the `Class.Workspace`, then select the `Class.Terrain` object.