fix: unmanagedFatal note

[Ithrael]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Modify the error message of unmanagedFatal a more understandable prompt while keeping consistency with unmanagedWarning‘s grammar.

Which issue(s) this PR fixes:

Fixes # kubernetes/kubectl#1467

Special notes for your reviewer:

Does this PR introduce a user-facing change?

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

[k8s-ci-robot]

Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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• ✅ login: Ithrael / name: Ithrael (63602f5)

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @Ithrael. 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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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Ithrael
Once this PR has been reviewed and has the lgtm label, please assign pwittrock for approval. For more information see the Kubernetes Code Review Process.

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