It’s tough to flunk the rational-basis test when a law that conceivably furthers a legitimate government interest and doesn’t step on a fundamental right is attacked as violating the U.S. Constitution’s equal protection clause. But 7th U.S. Circuit Court of Appeals Judges Amy St. Eve and Diane S. Sykes disagreed on whether St. Joan Antida High School’s challenge to the constitutionality of a Milwaukee Public School District regulation on free busing — which denied 68 of the school’s …