Correct the defined name of the parameter "micalg" in the documentation

The EVP_DigestInit(3) manual page contains wrong name for the define
macro for the OSSL_DIGEST_PARAM_MICALG param.

Fixes #23580

CLA: trivial

Reviewed-by: Paul Yang <kaishen.yy@antfin.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #23615)

(cherry picked from commit 5e5c256)

doc/man3/EVP_DigestInit.pod

@@ -490,7 +490,7 @@ EVP_MD_CTX_get_params() can be used with the following OSSL_PARAM keys:
 
 =over 4
 
-=item "micalg" (B<OSSL_PARAM_DIGEST_KEY_MICALG>) <UTF8 string>.
+=item "micalg" (B<OSSL_DIGEST_PARAM_MICALG>) <UTF8 string>.
 
 Gets the digest Message Integrity Check algorithm string. This is used when
 creating S/MIME multipart/signed messages, as specified in RFC 3851.