improve directory diff script

Author: mvorisek

.github/scripts/test-directory-unchanged.sh

@@ -3,8 +3,12 @@ set -ex
 
 cd "$(dirname "$0")/../../$1"
 
+# notify git about untracked files
+# add -f to detect even ignored files
+git add -N .
+
 # display overview of changed files
-git status
+git status .
 
-# display & detect all changes
-git add . -N && git diff --cached -a --exit-code . && git diff -a --exit-code .
+# display diff of working directory vs HEAD commit and set exit code
+git diff -a --exit-code HEAD .