Update test_versions to match current behaviour

xcube now puts its version number in xcube.__version__ and
xcube.version rather than xcube.version.version. test_versions.py
now accommodates this change.

Author: pont-us

test/util/test_versions.py

@@ -19,7 +19,7 @@ def test_it_contains_what_is_expected(self):
         self.assertIn('numpy', versions)
         self.assertIn('geopandas', versions)
         self.assertIn('xcube', versions)
-        self.assertEqual(xcube_version.version, versions['xcube'])
+        self.assertEqual(xcube_version, versions['xcube'])
 
     def test_it_is_cached(self):
         versions = get_xcube_versions()