Apply suggested fix to docs/api/cassandra/protocol.rst from Copilot Autofix

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

Author: 2 people

docs/api/cassandra/protocol.rst

@@ -16,7 +16,7 @@ holding custom key/value pairs.
 By default these are ignored by the server. They can be useful for servers implementing
 a custom QueryHandler.
 
-See :meth:`.Session.execute`, ::meth:`.Session.execute_async`, :attr:`.ResponseFuture.custom_payload`.
+See :meth:`.Session.execute`, :meth:`.Session.execute_async`, :attr:`.ResponseFuture.custom_payload`.
 
 .. autoclass:: _ProtocolHandler