This splits the CI Tests to one job per sub-directory in "tests/gem5"
via a matrix.
Advantages:
* We can utilize more runners to run the quick tests. This should mean
tests run quicker.
* This approach does not require editing of the workflow as more tests
are added or taken away.
* There is now an output artifact for each directory in "tests/gem5"
instead of one for the entriety of every quick test in "tests".
In addition:
* The artifact retention for the test outputs has been increased to 30 days.
* The output test artifacts have been renamed to be more descriptive of
the job, run, attempt, directory run, and the status.
* The 'tar' step has been removed. GitHub's 'action/artifact' can handle
directories.
Change-Id: I5b3132b424e3769d81d9cd75db2a8c59dbe4a7e5
561f3bd75b