One more attempt to fix preinst script for RPM and Debian

pkg/redhat/build.sh

@@ -71,8 +71,8 @@ The core server package for pgAdmin. pgAdmin is the most popular and feature ric
 rm -rf /usr/pgadmin4/venv
 if [ -d /usr/pgadmin4/web ]; then
   for f in /usr/pgadmin4/web/*; do
-    if [ "$f" != "/usr/pgadmin4/web/config_local.py" ]; then
-      rm -rf $f
+    if [ "${f}" != "/usr/pgadmin4/web/config_local.py" ]; then
+      rm -rf ${f}
     fi
   done
 fi