test: add tests for advance liability entries

Add Sales and Purchase Invoice Tests to check if GL entries and Outstanding Amount are generated correctly when advance entries are recorded as liability.

Few changes to return value of added column in Payment Entry References.
diff --git a/erpnext/accounts/utils.py b/erpnext/accounts/utils.py
index 506279c..c1d3653 100644
--- a/erpnext/accounts/utils.py
+++ b/erpnext/accounts/utils.py
@@ -625,6 +625,7 @@
 		if not d.exchange_gain_loss
 		else payment_entry.get_exchange_rate(),
 		"exchange_gain_loss": d.exchange_gain_loss,  # only populated from invoice in case of advance allocation
+		"account": d.account,
 	}
 
 	if d.voucher_detail_no: