Fixes:
- in uds tests, abort also silently on os errors
- be conservative on the h3 goaway duration
- detect curl debug build and use in checks
- fix caddy version check for slight difference under linux
- set caddy default path fitting for linux
- fix deprecation warnings in valid time checks
FTP tests:
- add '--with-test-vsftpd=path' to configure
- use vsftpd default path suitable for linux
- add test_30 with plain FTP tests
- add test_31 with --ssl-reqd FTP tests
- add vsftpd to linux GHA for pytest workflows
Closes#13661
345557248e