Fix html structure in mod_autoindex

[andrii-suse]

According to tidy utility, mod_autoindex generates incorrectly formatted html with ?F=1: https://github.com/andrii-suse/httpd/runs/1649928120?check_suite_focus=true#step:5:698

The fix is in 766396e , the other commit uses environs framework to show the problem in github actions above and that the fix really solves the problem in subsequent run (without breaking ?F=0 and ?F=2): https://github.com/andrii-suse/httpd/actions/runs/463409955

The httpd-test framework needs to be adjusted as well, e.g. with commit like this: https://github.com/andrii-suse/httpd-tests/commit/c7f69e9ab4d08c34a17184b977e91bda4db04a27

Feel free to accept only the fix commit, but environs framework is used in several projects to simplify integration and automation. I plan to add features covered with environs tests as well.