Fix inconsistency of placed feature locations

`BiomeSource#getBiomes` mixin applies to all biome sources, including one for Overworld.
The return value is a set; however one caller in the worldgen code iterates over it: `PlacedFeatureIndexer`.
Using a hash set here randomizes the return value, affecting feature placement.
Use a linked hash set instead.

fabric-biome-api-v1/src/main/java/net/fabricmc/fabric/mixin/biome/BiomeSourceMixin.java

@@ -17,7 +17,7 @@
 package net.fabricmc.fabric.mixin.biome;
 
 import java.util.Collections;
-import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.Set;
 import java.util.function.Supplier;
 
@@ -33,7 +33,7 @@
 public class BiomeSourceMixin {
 	@Redirect(method = "getBiomes", at = @At(value = "INVOKE", target = "Ljava/util/function/Supplier;get()Ljava/lang/Object;"))
 	private Object getBiomes(Supplier<Set<RegistryEntry<Biome>>> instance) {
-		var biomes = new HashSet<>(instance.get());
+		var biomes = new LinkedHashSet<>(instance.get());
 		fabric_modifyBiomeSet(biomes);
 		return Collections.unmodifiableSet(biomes);
 	}