Shareholders of Foundation Health Corp. of Rancho Cordova and Health Systems International of Woodland Hills approved the firms’ $1.34-billion merger, which would create the nation’s fourth-largest publicly held managed-care company. Foundation Health shareholders would own 61% of the new firm. The deal has not yet received state approval. The California Medical Assn. and a key state senator asked regulators to postpone the merger, contending it would be anti-competitive.