change 407 to 412

Change-Id: I1ca7e90ea7e6160e1cedf42c85c74237d631d90a
diff --git a/src/main/java/com/g9/g9backend/controller/UserController.java b/src/main/java/com/g9/g9backend/controller/UserController.java
index 7daf5f3..49dbd21 100644
--- a/src/main/java/com/g9/g9backend/controller/UserController.java
+++ b/src/main/java/com/g9/g9backend/controller/UserController.java
@@ -83,7 +83,7 @@
         if (userCheck != null) {
             // 用户名重复
             logger.warn("Registration attempt failed. Account already exists: {}", username);
-            return ResponseEntity.status(407).body("");
+            return ResponseEntity.status(412).body("");
         }
 
         // 查询邀请码是否存在