Tests in GitHub actions

[cfbolz]

try to get the unit tests to be run by github actions

[mattip]

test_multithread is failing on windows

================================== FAILURES ===================================
  _____________________________ test_multithreaded ______________________________

      def test_multithreaded():
          if '__pypy__' in sys.builtin_module_names:
              pytest.skip("not supported on pypy just yet")
          import threading
          finished = []

          def f():
              for k in range(1000):
                  l = [a for a in xrange(COUNT)]
              finished.append("foo")

          threads = [threading.Thread(target=f), threading.Thread(target=f)]
          prof = vmprof.Profiler()
  >       with prof.measure():

  vmprof\test\test_run.py:218: 

[cfbolz]

there are some flaky tests that segfault occasionally, that makes everything extra-annoying :-(