X509_EXTENSION_set_object.pod, X509v3_get_ext_by_NID.pod: add missing const

X509_EXTENSION_set_object.pod, X509v3_get_ext_by_NID.pod: add missing const

Update the documentation to include that added const qualifiers
to the arguments of X509_EXTENSION_get_object(), X509_EXTENSION_get_data(),
and X509v3_add_ext().

References: https://github.com/openssl/openssl/pull/30595
Complements: e75bd84ffc73 "Constify X509_get_ext() and friends.."
Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.foundation>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
MergeDate: Tue Mar 31 00:47:35 2026
(Merged from https://github.com/openssl/openssl/pull/30601)

(cherry picked from commit 0d5553fff4d1117c5380beaa8873ee9e8c56057e)