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_10_proxy.py

@@ -28,6 +28,7 @@ import filecmp
 import logging
 import os
 import re
+import sys
 import pytest
 
 from testenv import Env, CurlClient, ExecResult
@@ -179,6 +180,9 @@ class TestProxy:
                                   tunnel, fname, fcount):
         if tunnel == 'h2' and not env.curl_uses_lib('nghttp2'):
             pytest.skip('only supported with nghttp2')
+        if env.curl_uses_lib('mbedtls') and \
+           sys.platform.startswith('darwin') and env.ci_run:
+            pytest.skip('mbedtls 3.6.3 fails this test on macOS CI runners')
         count = fcount
         curl = CurlClient(env=env)
         url = f'https://localhost:{env.https_port}/{fname}?[0-{count-1}]'
@@ -209,6 +213,9 @@ class TestProxy:
                                     tunnel, fname, fcount):
         if tunnel == 'h2' and not env.curl_uses_lib('nghttp2'):
             pytest.skip('only supported with nghttp2')
+        if env.curl_uses_lib('mbedtls') and \
+           sys.platform.startswith('darwin') and env.ci_run:
+            pytest.skip('mbedtls 3.6.3 fails this test on macOS CI runners')
         count = fcount
         srcfile = os.path.join(httpd.docs_dir, fname)
         curl = CurlClient(env=env)
@@ -255,6 +262,9 @@ class TestProxy:
         # url twice via https: proxy separated with '--next', will reuse
         if tunnel == 'h2' and not env.curl_uses_lib('nghttp2'):
             pytest.skip('only supported with nghttp2')
+        if env.curl_uses_lib('mbedtls') and \
+           sys.platform.startswith('darwin') and env.ci_run:
+            pytest.skip('mbedtls 3.6.3 fails this test on macOS CI runners')
         curl = CurlClient(env=env)
         url = f'https://localhost:{env.https_port}/data.json'
         proxy_args = curl.get_proxy_args(tunnel=True, proto=tunnel)