WASHINGTON — The Supreme Court ruled Wednesday that government workers can’t be forced to contribute to labor unions that represent them in collective bargaining, dealing a serious financial blow to organized labor. The justices are scrapping a 41-year-old decision that had allowed states to require that public employees pay some fees to unions that represent them, even if the workers choose not to join. The 5-4 decision fulfills a longtime wish of conservatives to get rid of the so-called fair share fees that non-members pay to unions in roughly two dozen states.