fix data race in syncer test
fix data race in syncer test

[#96854664]

simonjjones/atc,pivotal-devin-fallak/atc,savaki/atc,pivotal-devin-fallak/atc,simonjjones/atc,savaki/atc,savaki/atc,utako/atc,pivotal-devin-fallak/atc,simonjjones/atc,zachgersh/atc,zachgersh/atc,zachgersh/atc,utako/atc,zachgersh/atc,utako/atc