[fix] SignUpCustomerRequest

- email 필드에 @notblank 추가
- 이메일이 "" 이어도 통과되는 문제 수정

src/main/java/camp/woowak/lab/web/dto/request/SignUpCustomerRequest.java

@@ -4,10 +4,12 @@
 
 import camp.woowak.lab.web.validation.annotation.Phone;
 import jakarta.validation.constraints.Email;
+import jakarta.validation.constraints.NotBlank;
 
 public record SignUpCustomerRequest(
 	@Length(min = 1, max = 50)
 	String name,
+	@NotBlank
 	@Email
 	String email,
 	@Length(min = 8, max = 20)