Remove Python 3.8 support

Python 3.8 is no longer be part of tested runtimes since 2024.2 and is
reaching its EOL soon. Bump the minimum supported python version.

Also declare Python 3.12 support because now it's part of the tested
runtimes.

Change-Id: Ib516cf3c83ede32db98add0416886dd58c7bef6b
Signed-off-by: Takashi Natsume <takanattie@gmail.com>

releasenotes/notes/remove-py38-e0701b3363079bbf.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

@@ -5,7 +5,7 @@ description_file = README.rst
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/os-vif/latest/
-python_requires = >=3.8
+python_requires = >=3.9
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -15,10 +15,10 @@ classifier =
     Programming Language :: Python
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3 :: Only
-    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
     Programming Language :: Python :: Implementation :: CPython
 
 [files]