Replace deprecated assertDictContainsSubset

The method is deprecated since Python 3.2[1] and shows the following
DeprecationWarning.

/usr/lib/python3.9/unittest/case.py:1134: DeprecationWarning:
assertDictContainsSubset is deprecated
  warnings.warn('assertDictContainsSubset is deprecated',

[1] https://docs.python.org/3/whatsnew/3.2.html#unittest

Closes-Bug: #1938103
Change-Id: I2e868d13d52a2d3c6081a8b756fbe83f8b57cf66
diff --git a/tempest/api/identity/admin/v3/test_domains.py b/tempest/api/identity/admin/v3/test_domains.py
index 32ccb9e..419c6c7 100644
--- a/tempest/api/identity/admin/v3/test_domains.py
+++ b/tempest/api/identity/admin/v3/test_domains.py
@@ -157,4 +157,4 @@
         self.addCleanup(self.delete_domain, domain['id'])
         expected_data = {'name': d_name, 'enabled': True}
         self.assertEqual('', domain['description'])
-        self.assertDictContainsSubset(expected_data, domain)
+        self.assertLessEqual(expected_data.items(), domain.items())