PEP 826: Set Python 3.16 status to 'planned' (#4853)

Author: hugovk

release_management/python-releases.toml

@@ -3634,7 +3634,7 @@ date = 2026-10-01
 
 [metadata."3.16"]
 pep = 826
-status = ""
+status = "planned"
 branch = ""
 release-manager = "Savannah Ostrowski"
 start-of-development = 2026-05-05