finalize python 3.9 support removal

The last release of openstack to support python 3.9
was 2025.1 (epoxy), with this change watcher-dashboard
now requires 3.10, testing of 3.9 was removed in previous
commits.

Change-Id: I7bad5281f6a36325f56038e7668ce584298ca888
Signed-off-by: Sean Mooney <work@seanmooney.info>

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

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    watcher-dashboard 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/watcher-dashboard/latest
-python_requires = >=3.9
+python_requires = >=3.10
 classifier =
     Development Status :: 5 - Production/Stable
     Environment :: OpenStack
@@ -20,7 +20,6 @@ classifier =
     Programming Language :: Python
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
     Programming Language :: Python :: 3.12