fix: pricing rule rounding

Consider a pricing rule of 20:1 with recursion enabled, free items
should follow the below progression

|   Qty | Free item qty |
|-------+---------------|
|  0-19 |             0 |
| 20-39 |             1 |
| 40-59 |             2 |

(cherry picked from commit 9bf3742)

erpnext/accounts/doctype/pricing_rule/utils.py

@@ -6,6 +6,7 @@
 
 import copy
 import json
+import math
 
 import frappe
 from frappe import _, bold
@@ -653,7 +654,7 @@ def get_product_discount_rule(pricing_rule, item_details, args=None, doc=None):
 		if transaction_qty:
 			qty = flt(transaction_qty) * qty / pricing_rule.recurse_for
 			if pricing_rule.round_free_qty:
-				qty = round(qty)
+				qty = math.floor(qty)
 
 	free_item_data_args = {
 		"item_code": free_item,