Maryland lawmakers moved forward a bill that would enable workers at Baltimore’s Walters Art Museum to form a union, the latest step in an ongoing organizing effort at the museum. “It’s the right step forward to save the Walters and help it flourish,” Baltimore Sen. Jill P. Carter said Friday, after her fellow senators agreed to advance legislation allowing workers to unionize. Baltimore’s members of the House of Delegates previously voted to support a slightly different version of the same bill.