Skip legacy TLS 1.0 tests if disabled by system. For example, this affects Fedora 36 installations which prohibit legacy TLS 1.0 connections by default. By today's standards, TLS 1.0 would be considered insecure, so it makes sense this is prohibited by default even if explicitly requested like in our test suite. Accordingly, this changeset only affects the test suite and has no effect on runtime.

For PHP, this can be reproduced (prior to applying this patch) by running the test suite in a default Fedora 36 installation like this:

$ docker run -it --rm -v `pwd`:/data --workdir=/data fedora:36 bash
# dnf install php-cli php-dom php-mbstring
# vendor/bin/phpunit

Resolves / closes #275
Builds on top of #229