[openssl/openssl] eab964: Clarify how to return string data

[Watson Ladd]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: eab96453bb145cde8e447f420a4ba099a5fa7004
      https://github.com/openssl/openssl/commit/eab96453bb145cde8e447f420a4ba099a5fa7004
  Author: Watson Ladd <watsonbladd at gmail.com>
  Date:   2023-05-25 (Thu, 25 May 2023)

  Changed paths:
    M doc/man3/OSSL_PARAM.pod

  Log Message:
  -----------
  Clarify how to return string data

Reviewed-by: Paul Dale <pauli at openssl.org>
Reviewed-by: Tomas Mraz <tomas at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21004)