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: Id7b02ca9c712c6e0c9b211f708dfcd5f18dd5336

releasenotes/notes/remove-py39-c25e3326fd1dfe86.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

@@ -7,7 +7,7 @@ author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/octavia-lib/latest/
 license = Apache License, Version 2.0
-python_requires = >=3.8
+python_requires = >=3.10
 classifier =
     Development Status :: 5 - Production/Stable
     Environment :: OpenStack
@@ -18,10 +18,9 @@ classifier =
     Operating System :: POSIX :: Linux
     Programming Language :: Python
     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 =

zuul.d/projects.yaml

@@ -9,5 +9,5 @@
       - octavia-tox-tips
     check:
       jobs:
-        - octavia-tox-functional-py39-tips:
+        - octavia-tox-functional-py311-tips:
             voting: false