fix style

Author: hkun0120

dolphinscheduler-alert/dolphinscheduler-alert-plugins/dolphinscheduler-alert-email/src/test/java/org/apache/dolphinscheduler/plugin/alert/email/ExcelUtilsTest.java

@@ -19,8 +19,6 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.apache.dolphinscheduler.plugin.alert.email.exception.AlertEmailException;
-
 import org.apache.poi.ss.usermodel.CellStyle;
 import org.apache.poi.ss.usermodel.Row;
 import org.apache.poi.ss.usermodel.Sheet;