Fixes vendored phpunit path issue #51

[shanept]

Continues the work done with the chmod-permission branch, fixing the resulting error related to incorrect filepaths to phpunit.

Here it is working in my CI. You will notice 4 different versions of phpunit used across the four different tests in the matrix. These phpunit instances are each installed by composer prior to the unit tests running.

[g105b]

Thank you @shanept , I will test this out and merge in soon. Looks good so far.