doc: add parameters for Http2Session:error event

Add parameters for the callback for the Http2Session:error event
inline with the pattern in the rest of the documentation.

Refs: nodejs/help#877 (comment)

PR-URL: nodejs#20206
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/api/http2.md

@@ -149,6 +149,8 @@ connected to the remote peer and communication may begin.
 added: v8.4.0
 -->
 
+* `error` {Error}
+
 The `'error'` event is emitted when an error occurs during the processing of
 an `Http2Session`.