Replace docker:// label-checker reference with docker run

[chagrafana]

Summary

• Replaces docker://agilepathway/pull-request-label-checker:latest with an equivalent docker run in a run: step
• The docker:// action format is incompatible with org-level action allowlist policies
• Same Docker image, same behavior, passes the same inputs via INPUT_ env vars

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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}