update-dependencies-github-action to avoid openig multiple PRs

[anegg0]

The cool src/scripts/update-variable-references.ts brings this repo closer to catching up with OCL's latest tools releases.
The only issue is that it can open multiple PRs (sometimes duplicative)

This PR is an attempt at improving the process by doing the following:

• First run: Creates branch docs/update-dependencies and PR with title "chore: update dependencies to latest versions"
• Subsequent runs: Find the existing open PR, update the branch with the latest changes, and update the PR body with current dependency information
• After PR is merged/closed: Next run will create a fresh PR since no open PR exists

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Project	Deployment	Preview	Updated (UTC)
arbitrum-docs	Ready	Preview	Sep 9, 2025 7:43pm

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Pull Request Overview

This PR improves the dependency update process by preventing multiple duplicate PRs. Instead of creating a new PR each time, the script now creates a single persistent branch and PR that gets updated with the latest dependency information.

Key changes:

• Creates a single persistent branch docs/update-dependencies and PR with standardized title
• Updates existing open PRs instead of creating new ones when dependencies change
• Adds backup branch creation to preserve commits when updating branches