They’re testing Knicks fans’ patience. Thousands of Big Apple teens will miss out on the Knicks historic ticker-tape parade down the Canyon of Heroes — because they’ll be stuck in class taking Regents exams. The scheduling snafu means students in the New York metro area will be stretching their brains while the rest of the city is losing their minds at the citywide victory celebration for the NBA champs on Thursday. “Honestly, it sucks,” said Jael Rosado, a freshman at LaGuardia High School in