[release-v0.53.x] Use a maintained action for "changed files"

[JeromeJu]

Changes

Cherry-pick for 0.53.x of 7407
And replace "dummy" with "sample" in go tests to make woke happy :)

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including functionality, content, code)
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• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

[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	92.6%	91.8%	-0.9
pkg/reconciler/taskrun/taskrun.go	85.2%	85.1%	-0.1

[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	92.6%	91.8%	-0.9
pkg/reconciler/taskrun/taskrun.go	85.2%	85.1%	-0.1

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dibyom

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[Yongxuanzhang]

/lgtm