[WIP] refactor fetching ClusterTask without TaskKind

[JeromeJu]

Changes

This commit is WIP to be separated from #6444 as a prerequisite.

/kind misc

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Release Notes

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[tekton-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[tekton-robot]

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[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage-df to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/taskrun/resources/taskref.go	89.7%	88.9%	-0.9

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/taskrun/resources/taskref.go	89.7%	88.9%	-0.9

[tekton-robot]

@JeromeJu: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-tekton-pipeline-unit-tests	8c9b7b1	link	true	/test tekton-pipeline-unit-tests

Full PR test history. Your PR dashboard.

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/test-infra repository. I understand the commands that are listed here.

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage-df to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/taskrun/resources/taskref.go	89.7%	88.9%	-0.9

[JeromeJu]

on second thoughts I realized the alternative is just to use hard-coded "clusterTask" string for comparison. Closing this if that would be easier not to cause confusion moving the ClusterTaskKind to v1.