No debug output when phar can't be downloaded

[blackwolf12333]

As you may have noticed, phpunit.de is being DDOS'ed right now which causes the phar download to fail. However this is not clear in the logs of the action so it took a while to figure out why the action is failing.

It would be useful in these cases to have some kind of output indicating the download failed.

Optionally it would be nice to not have to depend on phpunit.de being up for this action to work.

[blackwolf12333]

Or let users specify a path to a vendored phpunit script. We actually have it installed in the repo but the action is using the downloaded phar.