Fix GitHub Notifications plugin to support modern PAT tokens

[ywzheng1]

Summary

This PR fixes the GitHub Notifications xbar plugin rejecting valid GitHub personal access tokens.

Background

The plugin currently checks for tokens using len(token) == 40, which worked for classic PATs but no longer works with modern GitHub personal access tokens (e.g. github_pat_...) that are longer and now recommended by GitHub.

As a result, valid tokens are silently ignored and the plugin shows only a dot.

Changes

• Accept any non-empty GITHUB_TOKEN instead of assuming a fixed length
• Convert regex strings to raw strings to avoid Python SyntaxWarnings

Compatibility

• Classic 40-character tokens continue to work
• No behavior change when no token is set
• No API or UI changes

Testing

• Tested with classic PAT
• Tested with modern fine-grained github_pat_... token