Python: Expand test-filter tests

With no virtual environment enabled, none of the third-party library
test case are found.

python/ql/test/library-tests/filters/tests/Filter.expected

@@ -4,3 +4,5 @@
 | test_foo.py:3:1:3:15 | Function test_foo |
 | unittest_test.py:3:1:3:33 | Class FooTest |
 | unittest_test.py:4:5:4:25 | Function test_valid |
+| unittest_test.py:7:1:7:49 | Class FunctionFooTest |
+| unittest_test.py:8:5:8:25 | Function test_valid |

python/ql/test/library-tests/filters/tests/unittest_test.py

@@ -3,3 +3,29 @@ import unittest
 class FooTest(unittest.TestCase):
     def test_valid(self):
         pass
+
+class FunctionFooTest(unittest.FunctionTestCase):
+    def test_valid(self):
+        pass
+
+class AsyncTest(unittest.IsolatedAsyncioTestCase):
+    async def test_valid(self):
+        pass
+
+# django -- see https://docs.djangoproject.com/en/4.0/topics/testing/overview/
+import django.test
+class MyDjangoUnitTest(django.test.TestCase):
+    def test_valid(self):
+        pass
+
+# flask -- see https://pythonhosted.org/Flask-Testing/
+import flask_testing
+class MyFlaskUnitTest(flask_testing.LiveServerTestCase):
+    def test_valid(self):
+        pass
+
+# tornado -- see https://www.tornadoweb.org/en/stable/testing.html#tornado.testing.AsyncHTTPTestCase
+import tornado.testing
+class MyTornadoUnitTest(tornado.testing.AsyncHTTPTestCase):
+    def test_valid(self):
+        pass