By Silvia Ognibene and Valentina Za SIENA, Italy (Reuters) -Shareholders in Monte dei Paschi di Siena (MPS) on Thursday approved a new share sale for up to 2.5 billion euros ($2.5 billion), while doubts linger on whether the state-owned bank can pull off its latest cash call. Five years after a bailout that handed the state a 64% stake, MPS needs money to cut costs by shedding thousands of staff through costly early retirements and to replenish its capital buffers. Chief Executive Luigi Lovaglio said MPS would launch its seventh share issue in 14 years in October, while a new government is for…