caroot: Update certdata URL for GitHub switch

Mozilla has migrated its projects' source code to GitHub, update certdata URL
along with it.

Reference: https://github.com/curl/curl/pull/17321

Reviewed by: jrm (mentor), otis (mentor), kevans
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D50575

(cherry picked from commit 87c46facc3cf1744c30ecc9f63c10a778a1af104)