Due to an oversight, the PyUnit tests were not being run as part of the gem5 CI tests. This was because they are located in "tests/pyunit" instead of "tests/gem5", where the CI GitHub Action workflow searched for tests to run and where all other tests reside. This adds the Pyunit tests as a seperate job in the CI GitHub Action's workflow. Change-Id: I63d93571fde11c19bf3d281c034eddf4b455ae4e