fix(ci): set dependency PR service identity

[fqjony]

Summary

• set Docker dependency PR commit author to udx-github
• set Docker dependency PR committer to udx-github

Evidence

• udx-github user id: 73100442
• failed dependency run selected DEPENDABOT_REVIEWER_TOKEN but could not push: permission denied to udx-github

Validation

• git diff --check
• ruby YAML parse for docker-dependency-updater.yml

Follow-up outside this PR

• update the DEPENDABOT_REVIEWER_TOKEN PAT so it has repository access to udx/worker with Contents/Pull requests/Issues write

[Copilot]

Pull request overview

Updates the Docker dependency updater workflow so automated dependency PR commits are attributed to the udx-github service account, aligning commit metadata with the intended automation identity.

Changes:

• Set author for dependency update commits created via peter-evans/create-pull-request@v8 to udx-github.
• Set committer for those commits to udx-github.

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