test/api: fix white-space error

No double space between class methods, so say the scriptures.

test/mod/test_api.py

@@ -78,7 +78,6 @@ class TestAPI(unittest.TestCase):
             data = osbuild.api.arguments(path=path)
             self.assertEqual(data, args)
 
-
     def test_exception(self):
         # Check that 'api.exception' correctly sets 'API.exception'
         tmpdir = self.tmp.name