fix: concurrency issue leading to duplicate attendance insertion (#2041)

(cherry picked from commit b4db5ac)

hrms/hr/doctype/attendance/attendance.py

@@ -95,6 +95,7 @@ def get_duplicate_attendance_record(self) -> str | None:
 				& (Attendance.attendance_date == self.attendance_date)
 				& (Attendance.name != self.name)
 			)
+			.for_update()
 		)
 
 		if self.shift: