test: ut for parseServiceAccountToken

[cvvz]

What type of PR is this?
/kind test

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:

Release note:

none

[andyzhangx]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx, cvvz

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[andyzhangx]

/cherrypick release-1.26

[andyzhangx]

/cherrypick release-1.25

[k8s-infra-cherrypick-robot]

@andyzhangx: new pull request created: #1892

In response to this:

/cherrypick release-1.26

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@andyzhangx: new pull request created: #1893

In response to this:

/cherrypick release-1.25

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.