Fix incorrect link label

The specification for "OAuth 2.0 Token Exchange" is RFC 8693.
https://datatracker.ietf.org/doc/html/rfc8623 refers to a different specification,
so the current link is correct. This PR fixes the incorrect link label.

Author: koic

specification/draft/enterprise-managed-authorization.mdx

@@ -38,7 +38,7 @@ This profile is an application of the "Identity Assertion Authorization Grant" [
 The Identity Assertion Authorization Grant follows three steps:
 
 1. Single Sign-On to the MCP Client via OpenID Connect or SAML
-2. Token Exchange ([RFC8623](https://datatracker.ietf.org/doc/html/rfc8693))
+2. Token Exchange ([RFC8693](https://datatracker.ietf.org/doc/html/rfc8693))
 3. JWT Authorization Grant ([RFC7523](https://datatracker.ietf.org/doc/html/rfc7523))
 
 The core flow is as follows: