The North Penn School Board has approved a budget for the next school year.   The spending plan totals almost 208-million dollars and raises property taxes by 1.7%.   That translates into about $54 for the average homeowner.   District officials just last month were considering a tax increase about one-and-a-half times larger but School Board President Vince Sherpinsky says at least $100,000 more is coming from the state than originally anticipated.   He also says the district is getting a $750,000 windfall from a commercial property owner that has dropped a legal challenge of its tax assessment.