Update ko in release task to v0.12

[khrm]

ko is 0.7.0 in release and quite old. This updates it to the latest v0.12 available from our dogfooding registry.

Changes

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Release Notes

NONE

[khrm]

/kind misc

[alan-ghelardi]

/approve

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This pull-request has been approved by: alan-ghelardi

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[vdemeester]

/lgtm