SAN FRANCISCO — Warriors coach Steve Kerr tested positive for COVID-19 ahead of Game 4 of the Western Conference semifinals series against the Memphis Grizzlies. The news of Kerr entering the league’s health and safety protocols broke just two hours before tip-off Monday night. No one else on the Warriors has tested positive. Assistant coach Mike Brown will serve as the acting head coach in place of Kerr. Brown, who was just named the next head coach of the Sacramento Kings, served as Golden State’s acting head coach during a portion of the 2017 playoffs when Kerr was sidelined with a back iss…