postgresql: name of sources file fixed (update check) (#10854)

* fix: name of sources file fixed

The wrong name leads to updates being not possible as "No PostgreSQL Installation Found!" will be displayed.

* Change check for PostgreSQL installation commandupdate: switch from file to command check

* fix: command check expression

ct/postgresql.sh

@@ -23,7 +23,7 @@ function update_script() {
     header_info
     check_container_storage
     check_container_resources
-    if [[ ! -f /etc/apt/sources.list.d/pgdg.list ]]; then
+    if ! command -v psql >/dev/null 2>&1; then
         msg_error "No ${APP} Installation Found!"
         exit
     fi