Update: Implement "github" test system in the testing script.

Update: Implement "github" test system in the testing script.

The github actions has a repository that lacks cmocka.
Using the apt-get to download the systems cmocka library is slow and a waste of time.

Utilize the support for a custom "github" test system and manually download, compile, and install the cmocka source.
Given that this is for github, utilize a cmocka mirror repository that I found on github.
This is not ideal because it pulls from master rather than a specific version but it should work well enough.

Make any other appropriate changes or improvements to the testing script.