fix: missing minecraft version mapping

Author: NgLoader

zip-common/src/main/java/net/imprex/zip/common/MinecraftVersion.java

@@ -18,6 +18,7 @@ private static final class NmsMapping {
 		private static final List<NmsMapping> MAPPINGS = new ArrayList<>();
 
 		static {
+			MAPPINGS.add(new NmsMapping("1.21.9", "v1_21_R6"));
 			MAPPINGS.add(new NmsMapping("1.21.6", "v1_21_R5"));
 			MAPPINGS.add(new NmsMapping("1.21.5", "v1_21_R4"));
 			MAPPINGS.add(new NmsMapping("1.21.4", "v1_21_R3"));