fix: 修复flyway

backend/src/main/resources/db/migration/V39__modify_message_task_create_time.sql

@@ -1,2 +1,2 @@
-alter table message_task
+ALTER TABLE message_task
-    add create_time bigint(13) null;
+    ADD create_time bigint(13) DEFAULT 0;

backend/src/main/resources/db/migration/V41__modify_message_task_set.sql

@@ -1,3 +0,0 @@
-alter table message_task
-    alter column create_time set default 0;
-