load-fragment: downgrade log messages we ignore to LOG_WARNING

We typically don't log above LOG_WARNING about issues we then go on to
ignore. Do so here, too

src/core/load-fragment.c

@@ -4218,7 +4218,7 @@ int config_parse_exec_directories(
 
                 r = unit_full_printf(u, word, &k);
                 if (r < 0) {
-                        log_syntax(unit, LOG_ERR, filename, line, r,
+                        log_syntax(unit, LOG_WARNING, filename, line, r,
                                    "Failed to resolve unit specifiers in \"%s\", ignoring: %m", word);
                         continue;
                 }
@@ -4228,7 +4228,7 @@ int config_parse_exec_directories(
                         continue;
 
                 if (path_startswith(k, "private")) {
-                        log_syntax(unit, LOG_ERR, filename, line, 0,
+                        log_syntax(unit, LOG_WARNING, filename, line, 0,
                                    "%s= path can't be 'private', ignoring assignment: %s", lvalue, word);
                         continue;
                 }