close tsdb.head in test case (#9580)
close tsdb.head in test case (#9580)

Signed-off-by: Xiaochao Dong (@damnever) <534eb4447f79d39e46d634816fa3c5a272599cb0@gmail.com>
alileza/prometheus,alileza/prometheus,alileza/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,alileza/prometheus,prometheus/prometheus,alileza/prometheus,prometheus/prometheus,prometheus/prometheus,keegancsmith/prometheus,prometheus/prometheus,keegancsmith/prometheus,prometheus/prometheus