Auto add Platform: MacOS label when MacOS is picked in the issue (#2699)

## Description

Follow-up to
#2696

Author: j-piasecki

.github/workflows/platforms.yml

@@ -31,4 +31,4 @@ jobs:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           platforms-section-header: Platforms
           platforms-comma-separated: true
-          platforms-with-labels: '{"Android": "Platform: Android", "iOS": "Platform: iOS", "Web": "Platform: Web"}'
+          platforms-with-labels: '{"Android": "Platform: Android", "iOS": "Platform: iOS", "Web": "Platform: Web", "MacOS": "Platform: MacOS"}'