internal: allow python 3.9 and Plone 6

Author: erral

setup.py

@@ -23,8 +23,10 @@
         "Environment :: Web Environment",
         "Framework :: Plone",
         "Framework :: Plone :: Addon",
+        "Framework :: Plone :: 6.0",
         "Framework :: Plone :: 6.1",
         "Programming Language :: Python",
+        "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: 3.11",
         "Programming Language :: Python :: 3.12",