[openssl/openssl] 18f82d: Make link to RFC 1578 in CHANGES.md be a proper link

[Tomáš Mráz]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: 18f82df5b14b3fba078c6c5f0f4a0bb8eee6c954
      https://github.com/openssl/openssl/commit/18f82df5b14b3fba078c6c5f0f4a0bb8eee6c954
  Author: Tomas Mraz <tomas at openssl.org>
  Date:   2023-06-06 (Tue, 06 Jun 2023)

  Changed paths:
    M CHANGES.md

  Log Message:
  -----------
  Make link to RFC 1578 in CHANGES.md be a proper link

Reviewed-by: Tom Cosgrove <tom.cosgrove at arm.com>
Reviewed-by: Matt Caswell <matt at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21130)