MixinBlockBeaconAsyncUpdate: make the injection cancellable

this code has never worked, and nobody noticed because it was always throwing an exception on the stupid HTTP thread pool which gets used here for some reason, so the exception always got silently swallowed.

src/main/java/io/github/opencubicchunks/cubicchunks/core/asm/mixin/fixes/common/MixinBlockBeaconAsyncUpdate.java

@@ -51,7 +51,7 @@ public class MixinBlockBeaconAsyncUpdate {
     @Shadow(remap = false, aliases = "field_180358_a") @Final World val$worldIn;
     @Shadow(remap = false, aliases = "field_180357_b") @Final BlockPos val$glassPos;
 
-    @Inject(method = "run", at = @At("HEAD"))
+    @Inject(method = "run", at = @At("HEAD"), cancellable = true)
     private void runCubicChunks(CallbackInfo ci) {
         if (!((ICubicWorld) val$worldIn).isCubicWorld()) {
             return;