Remove remaining Python 3.9 support

Python 3.9 was removed from tested runtimes a few cycles ago and is
no longer supported globally.

Change-Id: I0d5db4d6a138dcee58834a0f2947d3af5b690bc6
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

setup.cfg

@@ -6,7 +6,7 @@ license = Apache License, Version 2.0
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 url = https://docs.openstack.org/python-designateclient/latest
-python_requires = >=3.9
+python_requires = >=3.10
 classifiers =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -17,10 +17,10 @@ classifiers =
     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
+    Programming Language :: Python :: 3.13
     Topic :: Internet :: Name Service (DNS)
 
 [files]

tox.ini

@@ -70,7 +70,7 @@ passenv = OS_STDOUT_CAPTURE
           OS_DEBUG
           TEMPEST_CONFIG
 
-[testenv:functional-py{39,310,311,312}]
+[testenv:functional-py{310,311,312,313}]
 setenv =
   {[testenv:functional]setenv}