finalize python 3.9 support removal

The last release of openstack to support python 3.9
was 2025.1 (epoxy), with this change watcherclient now
requires 3.10.

Change-Id: Iae0b4e113e149bca82c61c478c3cdf269057d0aa
Signed-off-by: Sean Mooney <work@seanmooney.info>

releasenotes/notes/drop-py39-8a9c99678b3e8eeb.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    watcher client now requires python 3.10 or newer.
+    The last release to support ``3.9`` was ``2025.1``.
+    Please ensure you have a supported python version before upgrading.

setup.cfg

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page =  https://docs.openstack.org/python-watcherclient/latest/
-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