docs: Fix .. value-table::

It does help if you actually check to see if the client supports a
given value!

docs/ext/capabilities.py

@@ -229,6 +229,9 @@ def get_client_support_for(self, capability: str):
 
             supported_values = set(supported_values)
             for value in clients[name]:
+                if value not in supported_values:
+                    continue
+
                 if (existing := clients[name][value]) is None:
                     clients[name][value] = version
                 else: