test: mark test-wasi-pthread as flaky

It has been flaking the CI for two months with no one working on
a fix. Mark it as flaky.

PR-URL: #59488
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>

Author: joyeecheung

test/wasi/wasi.status

@@ -14,3 +14,7 @@ test-wasi-getrusage: SKIP
 [$system==win32 || $system==android]
 # Unsupported on Windows and Android
 test-wasi-readdir: SKIP
+
+[$system==linux]
+# https://github.com/nodejs/node/issues/59146
+test-wasi-pthread: PASS, FLAKY