pytest: enable in 5 GHA jobs, fix fallouts

pytest: enable in 5 GHA jobs, fix fallouts

They take about 4.5 minutes of CI time in GHA/macos.

Also:
- autotools: improve `caddy`, `vsftpd` detection.
  Bringing it closer to cmake.
- autotools: fix `--with-test-caddy=no`, `--with-test-vsftps=no`,
  `--with-test-nghttpx=no` options.
- cmake: sync `nghttpx` default with autotools.
- pytest: disable failing mbedTLS tests on macOS CI.
- pytest: disable failing earlydata tests on macOS CI.
- GHA/macos: keep vsftpd pytests disabled due to lengthy run times.
- pytest: fix test_05_04 for LibreSSL. Ref: #17367
  Authored-by: Stefan Eissing
Remaining issues:
- some unidentified tests taking a long time with mbedTLS:
  `================= 462 passed, 278 skipped in 347.93s (0:05:47) =================`
  Ref: https://github.com/curl/curl/actions/runs/15073354301/job/42374999041#step:17:1536
  Workaround: not enabling pytest for mbedTLS jobs
- 17 FTP tests taking a long time (affecting all TLS backends):
  without vsftpd:
  `====================== 496 passed, 244 skipped in 56.15s =======================`
  Ref: https://github.com/curl/curl/actions/runs/15073354301/job/42374998230#step:17:1536
  with vsftpd:
  `================= 513 passed, 227 skipped in 409.37s (0:06:49) =================`
  Ref: https://github.com/curl/curl/actions/runs/15073678568/job/42376039672?pr=17362#step:17:1537
  Workaround: force-disable vsftpd.
- 100 tests failing with SecureTransport. Let's ignore that due to imminent deprecation.
  Ref: https://github.com/curl/curl/actions/runs/15055652333/job/42320873732#step:17:15362

Follow-up to 30ef79ed937ca0fc7592ff73d162398773c6a5aa #17295
Follow-up to 914790336664da0451e2f57906373a7707bd7cc3 #16518

Closes #17362