Drop Python 3.9 support

It was removed from tested runtimes in 2025.2 . It has been kept for
one cycle for smooth transition of the other projects, but it's time
to bump the enforced minimum requirement.

Also add Python 3.13 which has been tested for some time.

Change-Id: I539d34b9de8892c94e856da74bb8f25676562572
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

releasenotes/notes/remove-py39-e5ba2c03595b0756.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    Support for Python 3.9 has been removed. Now the minimum python version
+    supported is 3.10.

setup.cfg

@@ -6,7 +6,7 @@ summary = CADF Library
 description_file =
     README.rst
 home_page = https://docs.openstack.org/pycadf/latest/
-python_requires = >=3.9
+python_requires = >=3.10
 classifier =
     Development Status :: 5 - Production/Stable
     Environment :: OpenStack
@@ -17,10 +17,10 @@ classifier =
     Programming Language :: Python
     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
+    Programming Language :: Python :: 3.13
 
 [files]
 packages =