tests: fix a test job constaints failing in macOS

Allow scheduling mock job when running on MacOS (or Windows) hosts.

client/client_test.go

@@ -417,6 +417,8 @@ func TestClient_UpdateAllocStatus(t *testing.T) {
 	defer cleanup()
 
 	job := mock.Job()
+	// allow running job on any node including self client, that may not be a Linux box
+	job.Constraints = nil
 	job.TaskGroups[0].Count = 1
 	task := job.TaskGroups[0].Tasks[0]
 	task.Driver = "mock_driver"