fix: checkbox triggers get_items and sub_assembly buttons (#28558)

diff --git a/erpnext/manufacturing/doctype/production_plan/production_plan.js b/erpnext/manufacturing/doctype/production_plan/production_plan.js
index b171086..0babf87 100644
--- a/erpnext/manufacturing/doctype/production_plan/production_plan.js
+++ b/erpnext/manufacturing/doctype/production_plan/production_plan.js
@@ -238,6 +238,12 @@
 			method: "get_items",
 			freeze: true,
 			doc: frm.doc,
+			callback: function() {
+				frm.refresh_field("po_items");
+				if (frm.doc.sub_assembly_items.length > 0) {
+					frm.trigger("get_sub_assembly_items");
+				}
+			}
 		});
 	},