A young man previously banned from entering Brighton High School was arrested on Wednesday after fleeing from a school officer and being found with a gun on campus, police reported. Cottonwood Heights police indicated that the young man, whose identity was not revealed, entered the school located at 2200 Bengal Blvd. around 2:30 p.m. A school resource officer who saw him tried to approach, but the minor ran away, the police reported. Subsequentl…