macOS: Work around bug in system curl 8.{3,4,5} LibreSSL backend
Since !9500 (merged) CMake uses the macOS-provided curl, which uses the LibreSSL backend by default. This exposes us to curl issue 12525, created and fixed by the following upstream curl PRs:
- curl PR 11611, curl 8.3
- curl PR 12526, curl 8.6
Work around the bug by preferring the secure-transport backend by default on the problematic versions of curl.
Backport: release