Add python 3.13 testing and support

As per 2026.2 cycle testing runtime, python3.13 is
mandatory python version to test
- https://governance.openstack.org/tc/reference/runtimes/2026.1.html

Adding its testing and support in tempst.

Change-Id: Ifd1d2f8f8693e6269be98be9556acc53c8e52f4c
Signed-off-by: Ghanshyam Maan <gmaan@ghanshyammann.com>
diff --git a/setup.cfg b/setup.cfg
index 19e6289..fa17801 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -17,6 +17,7 @@
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
     Programming Language :: Python :: 3.12
+    Programming Language :: Python :: 3.13
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: Implementation :: CPython