fix: Assignment Rule Unassign Condition doesn't work (#24551)

Co-authored-by: Marica <maricadsouza221197@gmail.com>
Co-authored-by: Nabin Hait <nabinhait@gmail.com>
diff --git a/erpnext/selling/doctype/customer/customer.py b/erpnext/selling/doctype/customer/customer.py
index bf8b7fc..c452594 100644
--- a/erpnext/selling/doctype/customer/customer.py
+++ b/erpnext/selling/doctype/customer/customer.py
@@ -126,7 +126,9 @@
 		'''If Customer created from Lead, update lead status to "Converted"
 		update Customer link in Quotation, Opportunity'''
 		if self.lead_name:
-			frappe.db.set_value('Lead', self.lead_name, 'status', 'Converted', update_modified=False)
+			lead = frappe.get_doc('Lead', self.lead_name)
+			lead.status = 'Converted'
+			lead.save()
 
 	def create_lead_address_contact(self):
 		if self.lead_name: