Change yaml.load() to safe_load()

[sfowl]

Hardening measure to prevent issues with parsing crafted yaml:

https://pyyaml.org/wiki/PyYAMLDocumentation#loading-yaml

safe_load() will become the default in version 6.0:

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @sfowl. Thanks for your PR.

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[sfowl]

/kind cleanup
/cc @dims @liggitt @nikhita

[hwdef]

/ok-to-test
/release-note-none

[dims]

/sig-release
/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dims, sfowl

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[nikhita]

@sfowl thank you!

[nikhita]

/sig release