refactor: update min java version in fabric.mod.json to 21

Author: myoun

src/main/resources/fabric.mod.json

@@ -33,7 +33,7 @@
     "fabricloader": ">=${loader_version}",
     "fabric-api": "*",
     "minecraft": "~${minecraft_version}",
-    "java": ">=17",
+    "java": ">=21",
     "fabric-language-kotlin": ">=${fabric_kotlin_version}"
   },
   "suggests": {