Remove py39 jobs and reference from setup.cfg and jobs

Change-Id: I6fa3382b4a52e6bb0b00ed309d5b04c51e30a533

.zuul.yaml

@@ -21,7 +21,7 @@
         - neutron-tempest-plugin-tap-as-a-service
     periodic-weekly:
       jobs:
-        - openstack-tox-py39
+        - openstack-tox-py310
         - openstack-tox-py312
         - openstack-tox-py312-with-oslo-master
         - neutron-tempest-plugin-tap-as-a-service

releasenotes/notes/drop-py39-a1686919fc9d259b.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - |
+    Python 3.9 support has been dropped. The last release of neutron-vpnaas
+    to support py39 is Openstack 2025.1 (Epoxy).
+    For details about supported runtimes in Openstack 2025.2 please check:
+    https://governance.openstack.org/tc/reference/runtimes/2025.2.html

setup.cfg

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = http://www.openstack.org/
-python_requires = >=3.9
+python_requires = >=3.10
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -15,7 +15,6 @@ classifier =
     Operating System :: POSIX :: Linux
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
     Programming Language :: Python :: 3.12