fix(stock): make pick_list link query valid on Postgres (GROUP BY joined column)

get_pick_list_query selects Sales Order.customer (a joined table's column) while
grouping only by Pick List.name. Postgres' functional-dependency relaxation applies
to a table's own primary key, not to a joined table's columns, so the query raises
GroupingError on Postgres. MariaDB arbitrary-picks and runs.

customer is already pinned to a single value by `WHERE Sales Order.customer = filter`,
so adding it to the GROUP BY is identical on MariaDB and valid on Postgres.

Test (errors with GroupingError on the old code on Postgres, passes on both engines):
- test_get_pick_list_query_postgres_valid: a submitted pick list for a customer is
  returned by the link query.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

erpnext/stock/doctype/pick_list/pick_list.py

@@ -1372,7 +1372,10 @@ def get_pick_list_query(doctype: Any, txt: str, searchfield: Any, start: int, pa
 		.where(PICK_LIST.status.isin(["Open", "Partly Delivered"]))
 		.where(PICK_LIST.company == filters.get("company"))
 		.where(SALES_ORDER.customer == filters.get("customer"))
-		.groupby(PICK_LIST.name)
+		# customer is from the joined Sales Order, not Pick List's PK, so Postgres rejects it as a bare
+		# select under GROUP BY pick_list.name; it is pinned to one value by the filter above, so adding
+		# it to the GROUP BY is valid on Postgres and identical on MariaDB.
+		.groupby(PICK_LIST.name, SALES_ORDER.customer)
 	)
 
 	if filters.get("sales_order"):

erpnext/stock/doctype/pick_list/test_pick_list.py

@@ -1964,3 +1964,23 @@ class TestPickList(ERPNextTestSuite):
 				item_codes = [item.item_code for item in doc.items]
 				self.assertIn(item1, item_codes)
 				self.assertIn(item2, item_codes)
+
+	def test_get_pick_list_query_postgres_valid(self):
+		"""get_pick_list_query selects Sales Order.customer (a joined-table column) under
+		GROUP BY Pick List.name. Postgres rejects that bare column (PK functional dependency does
+		not cross tables), so the link query raised GroupingError. customer is pinned to one value
+		by the filter, so adding it to the GROUP BY is identical on MariaDB and valid on Postgres."""
+		from erpnext.stock.doctype.pick_list.pick_list import get_pick_list_query
+
+		warehouse = "_Test Warehouse - _TC"
+		item = make_item().name
+		make_stock_entry(item=item, to_warehouse=warehouse, qty=100, basic_rate=100)
+		so = make_sales_order(item_code=item, qty=5, rate=100)
+		pl = create_pick_list(so.name)
+		pl.submit()
+
+		# must run without raising on either engine (GroupingError on Postgres before the fix)
+		result = get_pick_list_query(
+			"Pick List", "", "name", 0, 20, {"company": so.company, "customer": so.customer}
+		)
+		self.assertIn(pl.name, [row["name"] for row in result])