Fix NSEC3HASH system test on jammy

a94aab9440 removed importorskip call from
isctest.name on which the functionality of this test relied.

Add an explicit importorskip call to the test.

bin/tests/system/tools/tests_tools_nsec3hash.py

@@ -19,6 +19,7 @@ from isctest.hypothesis.strategies import dns_names
 
 from hypothesis import strategies, given, settings
 
+pytest.importorskip("dns.dnssectypes")
 from dns.dnssectypes import NSEC3Hash
 import dns.dnssec