Error sweep: correct InvalidPipelineResultReference failure reason

[JeromeJu]

Pending: #7417 to be merged.

Changes

This commit corrects the PipelineRunReason which previously indicates
the invalid TaskResultReference to be its actual meaning which should be
InvalidPipelineResultReference.

/kind cleanup

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Release Notes

NONE

[tekton-robot]

Skipping CI for Draft Pull Request.
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[dibyom]

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dibyom, vdemeester

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[JeromeJu]

/retest