Update critical security release links.
This updates a few critical security release links that lead to defunct URLs so they lead to https://gitlab.com/gitlab-org/release/docs/blob/master/general/security/process.md#critical-security-releases instead.
Related:
- !35309 (merged) updates and adds code owners for security pages.
- !35398 (merged) updates the old "Critical Security Release Process" page but leaves it in place to avoid unexpected context-changing.
Edited by Brian Sexton