ruby/3.3: avoid direct ASN1_STRING accesses

[botovq]

openssl/openssl#29117

[botovq]

This is unlikely to be backported since maintenance branches accept bugfixes only. Anyone needing to use an old Ruby with OpenSSL 4.x should be able to skip the bundled openssl and later install a newer version via RubyGems. So let's fix it in master only for now.

ruby/openssl#978 (comment)