v1.18.1: fix a bug where spn: prefix is unexpectedly added to kubeconfig apiserver-id

[weinong]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind api-change
/kind bug
/kind cleanup
/kind deprecation
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:
fix a bug where spn: prefix is unexpectedly added to kubeconfig apiserver-id

Which issue(s) this PR fixes:

Fixes #89672

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

kubectl azure authentication: fixed a regression in 1.18.0 where "spn:" prefix was unexpectedly added to the `apiserver-id` configuration in the kubeconfig file

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

Hi @weinong. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[liggitt]

/ok-to-test
/priority critical-urgent
/milestone v1.18

[liggitt]

/retest
/lgtm
/approve

once this merges, can you open a cherry-pick to the release-1.18 branch?

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt, weinong

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[weinong]

/retest

[weinong]

/retest