gh-90473: Make chmod a dummy on WASI, skip chmod tests (GH-93534)

WASI does not have the ``chmod(2)`` syscall yet.

Modules/posixmodule.c

@@ -3282,6 +3282,10 @@ os_chmod_impl(PyObject *module, path_t *path, int mode, int dir_fd,
     {
 #ifdef HAVE_CHMOD
         result = chmod(path->narrow, mode);
+#elif defined(__wasi__)
+        // WASI SDK 15.0 does not support chmod.
+        // Ignore missing syscall for now.
+        result = 0;
 #else
         result = -1;
         errno = ENOSYS;