TBR: runner: Fix test flakiness
TBR: runner: Fix test flakiness

https://vanadium-review.googlesource.com/#/c/10624/ seems to have made
the integration tests flaky. I'm not quite sure I understand why
this change would make them less so, but trying this out
(presubmit run suggests that it might help)

Change-Id: If373483e40028c3c6ec2f15b5892dd0025b142fd

vanadium/browser,vanadium/browser,vanadium/browser,vanadium/browser