fix: updatable=false true 변경

Author: JunRain2

tuk-api/src/main/kotlin/nexters/tuk/domain/gathering/Gathering.kt

@@ -22,7 +22,7 @@ class Gathering private constructor(
 
     lastPushedAt: LocalDateTime?,
 ) : BaseEntity() {
-    @Column(name = "last_pushed_at", nullable = true, updatable = false)
+    @Column(name = "last_pushed_at", nullable = true)
     var lastPushedAt = lastPushedAt
         private set