Remove Python 3.8 support

Python 3.8 was removed from the tested runtimes for 2024.2[1] and has
not been tested since then.

Also add Python 3.12 which is part of the tested runtimes for 2025.1.
Now unit tests job with Python 3.12 is voting.

[1] https://governance.openstack.org/tc/reference/runtimes/2024.2.html

Change-Id: I50008cfcdd7745fb6f0273e10317023368e00d11

Author: kajinamit

releasenotes/notes/remove-py38-18af38f2ee386abc.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    Support for Python 3.8 has been removed. Now the minimum python version
+    supported is 3.9 .

setup.cfg

@@ -4,7 +4,7 @@ author = Mirantis
 author_email = mos-ironic@mirantis.com
 home_page = https://github.com/openstack/networking-generic-switch
 summary = Generic Switch ML2 Neutron Driver
-python_requires = >=3.8
+python_requires = >=3.9
 classifier =
     Development Status :: 3 - Alpha
     Environment :: OpenStack
@@ -16,10 +16,10 @@ classifier =
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3 :: Only
     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
 
 description_file =
     README.rst