run_wasi_tests.sh: Provide stdin by ourselves (#2576)

This improves test consistency between typical local environments and
github runners.

This is necessary for some of latest wasi-threads tests.

cf. 570e670631

tests/wamr-test-suites/wasi-test-script/pipe.py

@@ -0,0 +1,19 @@
+#! /usr/bin/env python3
+
+# Copyright (C) 2023 YAMAMOTO Takashi
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+# This is a copy of https://github.com/yamt/toywasm/blob/master/test/pipe.py
+
+# keep stdout open until the peer closes it
+
+import sys
+import select
+
+p = select.poll()
+p.register(sys.stdout, select.POLLHUP)
+# http://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=57369
+while True:
+    l = p.poll(1)
+    if l:
+        break