chore: update owlbot script to prevent silent failures at s.replace

[chelsea-lin]

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Fixes #<issue_number_goes_here> 🦕

[chelsea-lin]

Running the owl bot post processor locally:

docker pull gcr.io/cloud-devrel-public-resources/owlbot-python:latest
docker run --user $(id -u):$(id -g) --rm -v $(pwd):/repo -w /repo gcr.io/cloud-devrel-public-resources/owlbot-python:latest