Ignore .hypothesis files created by system tests

Some versions of the Hypothesis Python library - notably the one
included in stock OS repositories for Ubuntu 20.04 Focal Fossa - cause a
.hypothesis file to be created in a Python script's working directory
when the hypothesis module is present in its import chain.  Ignore such
files by adding them to the list of expected test artifacts to prevent
pytest teardown checks from failing due to these files appearing in the
file system after running system tests.

bin/tests/system/conftest.py

@@ -308,6 +308,7 @@ def logger(request, system_test_name):
 @pytest.fixture(scope="module")
 def expected_artifacts(request):
     common_artifacts = [
+        "*/.hypothesis",  # drop after Ubuntu 20.04 Focal Fossa gets removed from CI
         ".libs/*",  # possible build artifacts, see GL #5055
         "ns*/named.conf",
         "ns*/named.memstats",