Update workflow Emacs to 29.3

In an attempt to fix an issue generating Markdown on Emacs
28.2 (https://github.com/jeffkreeftmeijer/enough.css/blob/ca4d94b12abd60dcb8e19bc1a39b66d477b8f5a2/README.md?plain=1#L13-L22)
bump the version in the workflow to 29.3.

.github/workflows/readme.yml

@@ -18,7 +18,7 @@ jobs:
           fetch-depth: 0
       - uses: purcell/setup-emacs@master
         with:
-          version: 28.2
+          version: 29.3
       - run: emacs --batch enough.css.org --load scripts/readme.el/readme.el --eval "(readme/to-markdown \"README.md\")"
       - uses: stefanzweifel/git-auto-commit-action@v4
         with: