[openssl/openssl] f3e0df: Update the EVP_PKEY_get_id documentation

[Michael Baentsch]

  Branch: refs/heads/openssl-3.1
  Home:   https://github.com/openssl/openssl
  Commit: f3e0dfa742030bf3db356fd5fc22694fc485dbe7
      https://github.com/openssl/openssl/commit/f3e0dfa742030bf3db356fd5fc22694fc485dbe7
  Author: Michael Baentsch <57787676+baentsch at users.noreply.github.com>
  Date:   2023-03-25 (Sat, 25 Mar 2023)

  Changed paths:
    M doc/man3/EVP_PKEY_set1_RSA.pod
    M doc/man7/migration_guide.pod

  Log Message:
  -----------
  Update the EVP_PKEY_get_id documentation

The documentation didn't mention the development where EVP_PKEY_get_id()
returns a negative value for provider-only implementations, and the
migration guide didn't mention how to cope with that.

Fixes #20497

Reviewed-by: Tomas Mraz <tomas at openssl.org>
Reviewed-by: Richard Levitte <levitte at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20501)

(cherry picked from commit a2a543e0e3ec277d136772b4b0e0bb3d1181d337)