ci: clear release notes after v2.12.2 publish

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: mrdavearms

RELEASE_NOTES.md

@@ -11,5 +11,3 @@
        - **New feature name** — What it does and why teachers care.
        - **Fixed: bug description** — What was broken and how it's fixed.
 -->
-
-- **Fixed: "Check for Updates" no longer freezes on macOS** — the result used to appear in a pop-up that could hide behind the main window, making the app seem stuck. It now reports right under the button: "✓ You're on the latest version", or an "Update available" message with a **Download** button. No pop-up, no freeze.