missing SKIP_SLOW_TESTS (#13156)

* missing SKIP_SLOW_TESTS

this test took 2 seconds to execute on a 5GHz AMD Ryzen 9 7950x (one of AMD's fastest single-thread-performance CPUs), it should have SKIP_SLOW_TESTS

* skip message nitpick

ext/standard/tests/general_functions/proc_open_sockets1.phpt

@@ -1,5 +1,9 @@
 --TEST--
 proc_open() with output socketpairs
+--SKIPIF--
+<?php
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
+?>
 --FILE--
 <?php