Bump bungee to 1.21-R0.4 (#240)

Author: ItsNature

gradle/libs.versions.toml

@@ -5,7 +5,7 @@ adventure = "4.24.0"
 adventurePlatform = "4.4.1"
 artifactregistry = "2.2.1"
 bukkit = "1.8.8-R0.1-SNAPSHOT"
-bungee = "1.19-R0.1-SNAPSHOT"
+bungee = "1.21-R0.4"
 configurate = "4.2.0+lunar.5"
 geantyref = "1.3.11"
 idea = "1.1.7"