Update supported python versions

Python 3.9 was removed from the tested runtimes in this cycle[1].
Python 3.8 should have been removed in 2024.2 release.

Also declare support for Python 3.12 which has been tested for some
time and is mandatory now.

[1] https://governance.openstack.org/tc/reference/runtimes/2025.2.html

Change-Id: Ia7cf5ffe4e4093189fdee425afadd81df862be1e
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

Author: kajinamit

releasenotes/notes/remove-py39-8c71acfb47b84070.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    Support for Python 3.9 has been removed. Now Python 3.10 is the minimum
+    version supported.

setup.cfg

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/python-cloudkittyclient/latest/
-python_requires = >=3.8
+python_requires = >=3.10
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -17,10 +17,9 @@ classifier =
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.8
-    Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
+    Programming Language :: Python :: 3.12
 
 [files]
 packages =