Fix typo in docstring (pythonGH-23515)

Author: fernandohtr

Lib/http/client.py

@@ -861,7 +861,7 @@ def set_tunnel(self, host, port=None, headers=None):
         the endpoint passed to `set_tunnel`. This done by sending an HTTP
         CONNECT request to the proxy server when the connection is established.
 
-        This method must be called before the HTML connection has been
+        This method must be called before the HTTP connection has been
         established.
 
         The headers argument should be a mapping of extra HTTP headers to send