Remove Python 3.9 support

Python 3.9 is no longer part of the tested runtimes[1].

[1] https://governance.openstack.org/tc/reference/runtimes/2025.2.html

Change-Id: Ie96b62f758461369cf750eb5937ea890c3bf83c0
Co-authored-by: Takashi Kajinami <kajinamit@oss.nttdata.com>
Signed-off-by: Ivan Anfimov <lazekteam@gmail.com>

releasenotes/notes/remove-python39.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

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/trove/latest/
-python_requires = >= 3.9
+python_requires = >= 3.10
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -14,8 +14,9 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
+    Programming Language :: Python :: Implementation :: CPython
+    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
     Programming Language :: Python :: 3.12