fix: AlertMessage Equals&HashCode 추가

- 테스트 정상화를 위해 AlertMessage Equals&HashCode 추가

src/main/java/com/atwoz/alert/domain/vo/AlertMessage.java

@@ -3,10 +3,12 @@
 import jakarta.persistence.Embeddable;
 import lombok.AccessLevel;
 import lombok.AllArgsConstructor;
+import lombok.EqualsAndHashCode;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
 
 @Getter
+@EqualsAndHashCode
 @AllArgsConstructor(access = AccessLevel.PRIVATE)
 @NoArgsConstructor(access = AccessLevel.PROTECTED)
 @Embeddable