always use topmost/repo's .git as "--git-dir"

Author: mvorisek

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

@@ -1,13 +1,16 @@
 #!/bin/sh
 set -ex
 
-cd "$(dirname "$0")/../../$1"
+# use the repo root directory as "--git-dir"
+cd "$(dirname "$0")/../.."
+
+dir="$1"
 
 # notify git about untracked (except ignored) files
-git add -N .
+git add -N "$dir"
 
 # display overview of changed files
-git status .
+git status "$dir"
 
 # display diff of working directory vs HEAD commit and set exit code
-git diff -a --exit-code HEAD .
+git diff -a --exit-code HEAD "$dir"