Update MDK with new output from mod generator

Author: neoforge-mdk-automation[bot]

gradle.properties

@@ -18,7 +18,7 @@ minecraft_version=1.21.9
 # as they do not follow standard versioning conventions.
 minecraft_version_range=[1.21.9]
 # The Neo version must agree with the Minecraft version to get a valid artifact
-neo_version=21.9.8-beta
+neo_version=21.9.9-beta
 
 ## Mod Properties