Merge pull request #3873 from take-cheeze/fix_socket_test_leak

Fix memory leak found by leak sanitizer.

mrbgems/mruby-socket/test/sockettest.c

 #include <stdio.h>
+#include <stdlib.h>
 
 #include "mruby.h"
 
 mrb_value
 mrb_sockettest_tmppath(mrb_state *mrb, mrb_value klass)
 {
-  return mrb_str_new_cstr(mrb, tempnam(NULL, "mruby-socket"));
+  char *tmp = tempnam(NULL, "mruby-socket");
+  mrb_value str = mrb_str_new_cstr(mrb, tmp);
+  free(tmp);
+  return str;
 }
 
 void