WASHINGTON — The Supreme Court’s conservative majority appeared skeptical Friday of the Biden administration’s authority to impose a vaccine-or-testing requirement on the nation’s large employers. The court also was hearing arguments on a separate vaccine mandate for most health care workers.The arguments in the two cases come at a time of spiking coronavirus cases because of the omicron variant, and the decision Friday by seven justices to wear masks for the first time while hearing arguments reflected the new phase of …