Prepare for changes of su in util-linux 2.42

With util-linux 2.42 su gets more strict about it's command line.
From the release notes:
"pass arguments after <user> to shell (by cgoesche)"

It is also recommended to use "--login" instead of "-".

Could fix https://forum.checkmk.com/t/postgresql-services-disappear-after-updating-util-linux-to-2-42/58816

Author: mayrstefan

cmk/plugins/postgres/agents/mk_postgres.py

@@ -793,10 +793,10 @@ def _run_sql_as_db_user(
         # type: (str, str, str, bool, bool) -> str
         base_cmd_list = [
             "su",
-            "-",
-            self.db_user,
             "-c",
             r"""PGPASSFILE=%s %s -X %s -A0 -F'%s' -f %s""",
+            "--login",
+            self.db_user,
         ]
         extra_args += " -U %s" % self.pg_user
         extra_args += " -d %s" % self.pg_database
@@ -809,7 +809,7 @@ def _run_sql_as_db_user(
         if rows_only:
             extra_args += " -t"
 
-        base_cmd_list[-1] = base_cmd_list[-1] % (
+        base_cmd_list[-3] = base_cmd_list[-3] % (
             self.pg_passfile,
             self.psql_binary_path,
             extra_args,