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. Remove it as well as a few other older
versions which are no longer tested.

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: I7348d74210686f815cb791375c8d8c355a2da421

releasenotes/notes/remove-py38-c79328d063c6ea0b.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    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/manila-ui/latest/
-python_requires = >=3.6
+python_requires = >=3.9
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -17,12 +17,10 @@ classifier =
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
-    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 =