fix(deps): update dependency net.minecraftforge:forge to v1.21-51.0.16

Author: renovate[bot]

build.gradle

@@ -90,7 +90,7 @@ dependencies {
     // Specify the version of Minecraft to use, If this is any group other then 'net.minecraft' it is assumed
     // that the dep is a ForgeGradle 'patcher' dependency. And it's patches will be applied.
     // The userdev artifact is a special name and will get all sorts of transformations applied to it.
-    minecraft 'net.minecraftforge:forge:1.15.1-30.0.35'
+    minecraft 'net.minecraftforge:forge:1.21-51.0.16'
 
     // You may put jars on which you depend on in ./libs or you may define them like so..
     // compile "some.group:artifact:version:classifier"