build(ci): Add 'Needs Review' label to opened PRs

[david-allison]

⚠️ This change affects a pull_request_target workflow which is security critical. Please review carefully.

---

... unless they are drafts

This automates a task which maintainers could be pinged for

Fixes

• Fixes CI: Add 'Needs Review' label to opened PRs #19958

Approach

Add a workflow to labels.yml

Code is from

• CI: Automatically add 'Needs Review' label to newly opened PRs #19959
• f0b7671
• With thanks to @aladdin-afk

How Has This Been Tested?

• Added 'Needs Review' to my fork
• Pushed this commit to main
• non-draft: test david-allison/Anki-Android#46 ✅ label added
• draft: test - draft david-allison/Anki-Android#47 ✅ no label
• If the label already exists
  • https://github.com/david-allison/Anki-Android/actions/runs/20724944845/job/59498055490?pr=48
  • test: label already added david-allison/Anki-Android#48 ✅ no error

Checklist

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[mikehardy]

LGTM