use git diff --cached in diff check action

ensures every build difference is in the diff

.github/workflows/check-dist.yml

@@ -38,9 +38,9 @@ jobs:
 
       - name: Compare the expected and actual dist/ directories
         run: |
-          if [ "$(git diff --ignore-space-at-eol dist/ | wc -l)" -gt "0" ]; then
+          if [ "$(git diff --cached --ignore-space-at-eol dist/ | wc -l)" -gt "0" ]; then
             echo "Detected uncommitted changes after build.  See status below:"
-            git diff
+            git diff --cached --ignore-space-at-eol dist/
             exit 1
           fi
         id: diff