[CI] Increase migration test coverage (#6995)

* also trigger CI on changes to test files

* dummy change to test file

* fix match pattern

.github/workflows/qc_checks.yaml

@@ -48,6 +48,7 @@ jobs:
               - 'src/backend/requirements.txt'
               - 'src/backend/requirements-dev.txt'
             migrations:
+              - '**/test_migrations.py'
               - '**/migrations/**'
               - '.github/workflows**'
               - 'src/backend/requirements.txt'

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)