Fixes set_x509_certificate_chain() and x509_certificate_chain() implementation error.
Per RFC 7515, 4.1.6 (https://datatracker.ietf.org/doc/html/rfc7515#section-4.1.6) each string entry in the x5c header parameter is a "base64-encoded (Section 4 of [RFC4648] -- not base64url-encoded) DER [ITU.X690.2008] PKIX certificate value."
Fixes set_x509_certificate_chain() and x509_certificate_chain() implementation error.
Per RFC 7515, 4.1.6 (https://datatracker.ietf.org/doc/html/rfc7515#section-4.1.6) each string entry in the x5c header parameter is a "base64-encoded (Section 4 of [RFC4648] -- not base64url-encoded) DER [ITU.X690.2008] PKIX certificate value."