doc: fix error description of the max header size

PR-URL: #54125
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/errors.md

@@ -3196,7 +3196,7 @@ changes:
 -->
 
 Too much HTTP header data was received. In order to protect against malicious or
-malconfigured clients, if more than 8 KiB of HTTP header data is received then
+malconfigured clients, if more than `maxHeaderSize` of HTTP header data is received then
 HTTP parsing will abort without a request or response object being created, and
 an `Error` with this code will be emitted.