[release-0.16] scripts/update-gh-pages: fix release version parsing

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #1974

/assign marquiz

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[k8s-ci-robot]

@k8s-infra-cherrypick-robot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-node-feature-discovery-build-image-relese-0-16	2a5ea0a	link	true	/test pull-node-feature-discovery-build-image-relese-0-16
pull-node-feature-discovery-build-image-cross-generic	2a5ea0a	link	true	/test pull-node-feature-discovery-build-image-cross-generic

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[marquiz]

Need to combine all the related backports in #1980
/close

[k8s-ci-robot]

@marquiz: Closed this PR.

In response to this:

Need to combine all the related backports in #1980
/close

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