fix: Document Type as CHL in case of return Invoice with Nil-rated (#…

…2028)

**Issue**
Document type was mapped incorrect in case of Sales and Purchase Return.

**Before**

https://github.com/resilient-tech/india-compliance/assets/54097382/7778eba7-0692-4b1d-867c-bbd9375162b1

**After**

https://github.com/resilient-tech/india-compliance/assets/54097382/d2f65194-4447-4235-a85a-5918e7b8c000

(cherry picked from commit 2a34abf)

india_compliance/gst_india/utils/e_waybill.py

@@ -1473,9 +1473,13 @@ def update_transaction_details(self):
             if not doc.is_export_with_gst:
                 self.transaction_details.update(document_type="BIL")
 
-        if doc.doctype in ("Sales Invoice", "Purchase Invoice") and all(
-            item.gst_treatment in ("Nil-Rated", "Exempted", "Non-GST")
-            for item in doc.items
+        if (
+            doc.doctype in ("Sales Invoice", "Purchase Invoice")
+            and not doc.is_return
+            and all(
+                item.gst_treatment in ("Nil-Rated", "Exempted", "Non-GST")
+                for item in doc.items
+            )
         ):
             self.transaction_details.update(document_type="BIL")