Update git check to look for staged differences when updating events

Fixes #714

Author: JarrodCTaylor

.github/workflows/publish-events.yml

@@ -39,7 +39,7 @@ jobs:
           git config --global user.name clojure-build
           git config --global user.email "[email protected]"
           git add content/events
-          if git status | grep -q modified
+          if ! git diff --quiet --cached
           then
               git commit -m 'update events'
               git push