Swarming bots: Fix tester out dir

TBR=rmistry
NOTRY=true
BUG=skia:4763
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1751463002

Review URL: https://codereview.chromium.org/1751463002
1 file changed