gh-110974: Make sure all test_zoneinfo tests are collected (GH-110975)

Test classes from the test_zoneinfo submodule were overridden by
test classes from the test_zoneinfo_property submodule with the same name.

Author: sobolevn

Lib/test/test_zoneinfo/__init__.py

@@ -1,2 +1,5 @@
-from .test_zoneinfo import *
-from .test_zoneinfo_property import *
+import os
+from test.support import load_package_tests
+
+def load_tests(*args):
+    return load_package_tests(os.path.dirname(__file__), *args)