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 30ef79ed93 #17295
Follow-up to 9147903366 #16518

Closes #17362

tests/http/test_05_errors.py

@@ -118,10 +118,11 @@ class TestErrors:
         url = f'https://{env.authority_for(env.domain1, proto)}'\
             f'/curltest/shutdown_unclean?id=[0-{count-1}]&chunks=4'
         r = curl.http_download(urls=[url], alpn_proto=proto, extra_args=[
-            '--parallel',
+            '--parallel', '--trace-config', 'ssl'
         ])
         if proto == 'http/1.0' and not env.curl_uses_lib('wolfssl') and \
-                (env.curl_is_debug() or not env.curl_uses_lib('openssl')):
+                (env.curl_is_debug() or
+                not env.curl_uses_any_libs(['openssl', 'libressl'])):
             # we are inconsistent if we fail or not in missing TLS shutdown
             # openssl code ignore such errors intentionally in non-debug builds
             r.check_exit_code(56)