Stop requiring pytest-subtests for python>3.9, it has been incorporated into pytest (#115)

Author: StanFromIreland

tox.ini

@@ -6,8 +6,9 @@ skip_missing_interpreters = true
 [testenv]
 description = Test that the tzdata contents are accessible
 deps =
-    pytest
-    pytest-subtests; python_version>='3.6'
+    pytest >= 9; python_version >= '3.10'
+    pytest; python_version < '3.10'
+    pytest-subtests; python_version >= '3.6' and python_version <= '3.9'
     importlib_resources; python_version<'3.7'
 commands =
     pytest {toxinidir} {posargs}