Update sales_taxes_and_charges.json

Change Rate label to existing Tax Rate label so it can be correctly translated in other languages

(cherry picked from commit 2b93be1139bcb963a89c10f261a1dd2c83f01980)

erpnext/accounts/doctype/sales_taxes_and_charges/sales_taxes_and_charges.json

@@ -108,7 +108,7 @@
    "fieldname": "rate",
    "fieldtype": "Float",
    "in_list_view": 1,
-   "label": "Rate",
+   "label": "Tax Rate",
    "oldfieldname": "rate",
    "oldfieldtype": "Currency"
   },
@@ -227,4 +227,4 @@
  "sort_field": "modified",
  "sort_order": "ASC",
  "states": []
-}
+}