chore(ci): prevent duplicate container upgrade PRs

[gnodet]

Summary

Fix the check-container-versions.yml workflow to avoid creating duplicate PRs for the same container version upgrade.

Problem

The workflow was creating duplicate PRs (e.g., #21822 and #21895 both upgrade ollama to 0.17.7) because:

1. The branch name included ${{ github.run_number }}, making each weekly run create a unique branch even for the same upgrade
2. There was no check for existing open PRs before creating a new one

Fix

Two changes:

1. Deterministic branch names: Remove the run number suffix. Branch names are now automated/upgrade-<property>-<version> (e.g., automated/upgrade-ollama-container-0.17.7). If a PR for the same property+version already exists, git push will be a no-op (same content) or fail gracefully.

2. Check for existing open PRs: Before creating a branch/PR, the workflow now checks:

   • Whether an open PR with the same branch name already exists (exact same upgrade)
   • Whether any open PR with the container-images label already exists for the same property name (different version of the same container)

   In either case, the upgrade is skipped with a log message.

Example

Before: Running the workflow twice in a week with ollama outdated would create:

• automated/upgrade-ollama-container-0.17.7-16 (run 16)
• automated/upgrade-ollama-container-0.17.7-17 (run 17) — duplicate!

After: The second run detects the existing PR and skips it.

[github-actions]

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