http: reset headers timeout on headers complete

headers timeout should not occur *after* headers have been
received.

Fixes: https://github.com/nodejs/node/issues/34576

PR-URL: https://github.com/nodejs/node/pull/34578


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Pranshu Srivastava <rexagod@gmail.com>