Cleveland Browns center JC Tretter, the NFL Players Association president who has been pushing the league for daily COVID-19 testing all season, tested positive for the virus on Thursday. So did Vikings running back Dalvin Cook. But Washington is getting back quarterback Taylor Heinicke. Tretter posted on Twitter that he was experiencing symptoms and chose to be tested at the team’s facility in Berea, Ohio. “Unfortunately, I am positive for COVID-19,” Tretter wrote. “I encourage all NFL players to take every precaution available to them to protect themselves, their families and their teammates from this virus.” The Browns have been hit hard by a spate of positive tests in the past week and were missing 22 players, including Baker Mayfield as well as coach Kevin Stefanski, for Monday night’s rescheduled game against Las Vegas, which Cleveland lost. On Wednesday, Tretter spoke to reporters for the first time in weeks and …