[CI] Increase migration test coverage (#6995)

* also trigger CI on changes to test files

* dummy change to test file

* fix match pattern

src/backend/InvenTree/stock/test_migrations.py

@@ -64,6 +64,7 @@ class TestSerialNumberMigration(MigratorTestCase):
             big_ref_item.serial,
             '9999999999999999999999999999999999999999999999999999999999999',
         )
+
         self.assertEqual(big_ref_item.serial_int, 0x7FFFFFFF)