t: warn against adding non-httpd-specific tests after sourcing 'lib-httpd'

t: warn against adding non-httpd-specific tests after sourcing 'lib-httpd'

We have a couple of test scripts that are not completely
httpd-specific, but do run a few httpd-specific tests at the end.
These test scripts source 'lib-httpd.sh' somewhere mid-script, which
then skips all the rest of the test script if the dependencies for
running httpd tests are not fulfilled.

As the previous two patches in this series show, already on two
occasions non-httpd-specific tests were appended at the end of such
test scripts, and, consequently, they were skipped as well when httpd
tests couldn't be run.

Add a comment at the end of these test scripts to warn against adding
non-httpd-specific tests at the end, in the hope that they will help
prevent similar issues in the future.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>