test: clear singles cache for changed settings (#29430)

diff --git a/erpnext/tests/utils.py b/erpnext/tests/utils.py
index bc9f04e..2bd7e9e 100644
--- a/erpnext/tests/utils.py
+++ b/erpnext/tests/utils.py
@@ -92,6 +92,8 @@
 		for key, value in settings_dict.items():
 			setattr(settings, key, value)
 		settings.save()
+		# singles are cached by default, clear to avoid flake
+		frappe.db.value_cache[settings] = {}
 		yield # yield control to calling function
 
 	finally: