pkgconf: match the update to version 2.9.93

This update brings spdxtool(1), with the ability to generate software
bill of material files (SBOM) in the SPDX 3.0.1 format (JSON-LD).

Reviewed by: markj
Approved by: markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D57953