fix(workflow): push screenshots-commit using GITHUB_TOKEN to avoid 403

[vitorvasc]

The PR Screenshots - Commit workflow has been returning HTTP 403 on git push origin otelbot/screenshots (example).

• actions/checkout no longer passes a token: input, so it falls back to GITHUB_TOKEN. The push at git push origin otelbot/screenshots now authenticates with GITHUB_TOKEN, which has contents: write from the job-level permissions: block.
• Uses the same pattern as nightly-registry-update.yml already uses to push to otelbot/automated-inventory-update.
• The Get otelbot token step moves to immediately before Post or update PR comment, where its token is consumed via GH_TOKEN for the gh api calls.

[netlify]

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[Copilot]

Pull request overview

Adjusts the “PR Screenshots - Commit” GitHub Actions workflow authentication so the screenshots branch push uses the job’s GITHUB_TOKEN (with contents: write) instead of a GitHub App token, resolving the observed git push 403 failures. The GitHub App token step is retained but moved to just-in-time usage for gh api comment updates.

Changes:

• Removed the GitHub App token from actions/checkout, letting it default to GITHUB_TOKEN for authenticated git push to otelbot/screenshots.
• Moved the “Get otelbot token” step to immediately before the PR comment update step, and wired it via GH_TOKEN for gh api.