Tests: Include limits.h for PATH_MAX in realpath tests

Author: https://github.com/timschumi
Commit: 8ebc749191
Pull-request: https://github.com/SerenityOS/serenity/pull/12949

Tests/LibC/TestRealpath.cpp

@@ -9,6 +9,7 @@
 #include <AK/String.h>
 #include <AK/StringBuilder.h>
 #include <errno.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>