.github/workflows/update.yml: Prevent errors

Author: bzg

.github/workflows/update.yml

@@ -29,5 +29,5 @@ jobs:
           git config --local user.email "bastien.guerry@code.gouv.fr"
           git config --local user.name "Bastien Guerry"
           git add README.md
-          git commit -m "Update README from http://code.gouv.fr/data/awesome-codegouvfr.md"
+          git diff --quiet || (git commit -m "Update README from http://code.gouv.fr/data/awesome-codegouvfr.md")
           git push -f origin main