testing: install setuptools to fix pkg_resources import in a test

Since Python 3.12, setuptools is no longer installed by default in
venvs. We have a test which uses it, so add it to the testing extra.

Author: bluetech

setup.cfg

@@ -73,6 +73,7 @@ testing =
     nose
     pygments>=2.7.2
     requests
+    setuptools
     xmlschema
 
 [options.package_data]