By Richard Cowan and Makini Brice WASHINGTON (Reuters) -U.S. Senate Democrats on Saturday were set to push ahead on a bill that would address key elements of President Joe Biden’s agenda – tackling climate change, lowering the cost of energy and elderly people’s medications and forcing some corporations and wealthy Americans to pay more taxes. The Senate parliamentarian determined that the lion’s share of the healthcare provisions in the $430 billion bill could be passed with only a simple majority, bypassing a filibuster rule requiring 60 votes in the 100-seat chamber to advance most legislat…