doc: add params for ClientHttp2Session:altsvc

Add parameters for the callback for the ClientHttp2Session:altsvc
event inline with the pattern in the rest of the documentation.

Refs: nodejs/help#877 (comment)

PR-URL: #20598
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/http2.md

@@ -664,9 +664,9 @@ added: v8.4.0
 added: v9.4.0
 -->
 
-* `alt`: {string}
-* `origin`: {string}
-* `streamId`: {number}
+* `alt` {string}
+* `origin` {string}
+* `streamId` {number}
 
 The `'altsvc'` event is emitted whenever an `ALTSVC` frame is received by
 the client. The event is emitted with the `ALTSVC` value, origin, and stream