scripts: Allow checkShellScripts.sh to be run from its parent directory

... on systems that don't have realpath.

Part of 31679.

scripts/maint/checkShellScripts.sh

@@ -21,7 +21,7 @@ if command -v realpath ; then
     HERE=$(dirname "$(realpath "$0")")
 else
     HERE=$(dirname "$0")
-    if [ ! -d "$HERE" ]; then
+    if [ ! -d "$HERE" ] || [ "$HERE" = "." ]; then
         HERE=$(dirname "$PWD/$0")
     fi
 fi