Require pytz only in Python < 3.9

ptyz is no longer required in Python >= 3.9 in favor of zoneinfo.

Also tzdata was added to requirements as a runtime dependency of
zoneinfo, which is only available in Python >= 3.9 and is not required
in Python 3.8.

Depends-on: https://review.opendev.org/c/openstack/requirements/+/901119
Change-Id: Icb5bffbeb3da0582332c420ec2b4ceac1a58966b

requirements.txt

@@ -10,5 +10,5 @@
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 msgpack>=0.5.2 # Apache-2.0
 oslo.utils>=3.33.0 # Apache-2.0
-pytz>=2013.6 # MIT
-tzdata>=2022.4 # MIT
+pytz>=2013.6;python_version<"3.9" # MIT
+tzdata>=2022.4;python_version>="3.9" # MIT