Fix inconsistency in auto-update-pull-request.yml to use standard otelbot configuration

[Copilot]

Summary

This PR fixes an inconsistency in the auto-update-pull-request.yml workflow where it was using non-standard secret and variable names for the otelbot GitHub App configuration.

Changes Made

• Fixed secret name: Changed OTELBOT_JAVA_INSTRUMENTATION_PRIVATE_KEY to OTELBOT_PRIVATE_KEY to match all other workflows
• Fixed app-id: Changed hardcoded app-id: 1295839 to ${{ vars.OTELBOT_APP_ID }} to match all other workflows

Context

The migration from opentelemetrybot to otelbot was mostly complete across the repository, but this one workflow file had inconsistent naming that didn't match the standard pattern used by all other workflows:

Before:

- uses: actions/create-github-app-token@df432ceedc7162793a195dd1713ff69aefc7379e
  id: otelbot-token
  with:
    app-id: 1295839
    private-key: ${{ secrets.OTELBOT_JAVA_INSTRUMENTATION_PRIVATE_KEY }}

After:

- uses: actions/create-github-app-token@df432ceedc7162793a195dd1713ff69aefc7379e
  id: otelbot-token
  with:
    app-id: ${{ vars.OTELBOT_APP_ID }}
    private-key: ${{ secrets.OTELBOT_PRIVATE_KEY }}

Verification

• ✅ All workflows now consistently use ${{ vars.OTELBOT_APP_ID }} for app-id
• ✅ All workflows now consistently use ${{ secrets.OTELBOT_PRIVATE_KEY }} for private-key
• ✅ YAML syntax validated
• ✅ No remaining references to old opentelemetrybot patterns found

This ensures consistency across all GitHub App token generation in the repository's workflows.

Fixes #34.

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