Update style guide action to v0.5

- Update from @v0.3 to @v0.5
- Latest version includes:
  - Production testing infrastructure
  - PR labels feature
  - Simplified @qe-style-checker syntax
  - Bug fixes and improvements

See: https://github.com/QuantEcon/action-style-guide/releases/tag/v0.5.0

Author: mmcky

.github/workflows/style-guide.yml

@@ -10,10 +10,10 @@ jobs:
     if: contains(github.event.comment.body, '@qe-style-checker')
     runs-on: ubuntu-latest
     steps:
-      - uses: QuantEcon/action-style-guide@v0.3
+      - uses: QuantEcon/action-style-guide@v0.5
         with:
           mode: 'single'
           lectures-path: 'lectures/'
           anthropic-api-key: ${{ secrets.ANTHROPIC_API_KEY }}
           github-token: ${{ secrets.GITHUB_TOKEN }}
-          comment-body: ${{ github.event.comment.body || github.event.issue.body }}
+          comment-body: ${{ github.event.comment.body || github.event.issue.body }}