The House on Friday passed a $1.2 trillion spending bill to fund the government through September and avert a partial shutdown at the end of the week, setting off a G.O.P. mutiny that threatened Speaker Mike Johnson’s grasp on the gavel.In a 286-134 vote that came down to the wire, Democrats rallied to provide the support to overcome a furious swell of opposition by conservative Republicans. Infuriated by the painstakingly negotiated bipartisan legislation to keep funding flowing for government agencies including the Pentagon and the Department of Homeland Security, the hard right…