chore: fix kokoro config for samples (#817)

Source-Link: https://github.com/googleapis/synthtool/commit/dd05f9d12f134871c9e45282349c9856fbebecdd
Post-Processor: gcr.io/repo-automation-bots/owlbot-python:latest@sha256:aea14a583128771ae8aefa364e1652f3c56070168ef31beb203534222d842b8b

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
5 files changed