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: I848996fa6d35d0dddb3f9001977637ec4a752eda

releasenotes/notes/remove-py38-9ff5e159cfa29d23.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

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/python-cinderclient/latest/
-python_requires = >=3.8
+python_requires = >=3.9
 classifier =
     Development Status :: 5 - Production/Stable
     Environment :: Console
@@ -21,6 +21,7 @@ classifier =
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
+    Programming Language :: Python :: 3.12
 
 [files]
 packages =

tox.ini

@@ -107,7 +107,7 @@ setenv =
 # TLS (https) server certificate.
 passenv = OS_*
 
-[testenv:functional-py{3,38,39,310,311,312}]
+[testenv:functional-py{3,39,310,311,312}]
 deps = {[testenv:functional]deps}
 setenv = {[testenv:functional]setenv}
 passenv = {[testenv:functional]passenv}