A man accused of robbing two Lake Tahoe banks in 2010 pleaded guilty to a string of Northern California bank hold-ups Friday.Former Carson City resident David Griffith Osborne, 74, pleaded guilty in federal court in Sacramento to three counts of armed robbery in connection with bank heists in Gridley, Rancho Cordova and Paradise.He will serve just more than 10 years in prison if a judge approves a plea agreement with prosecutors.In the agreement Osborne also admitted to robbing Bank of the West branches in Kings Beach and South Lake Tahoe and two robberies of the same Bank of the West …