wasi: fixes os.isatty on type mismatch (#13813)

lib/std/os.zig

@@ -3158,7 +3158,7 @@ pub fn isatty(handle: fd_t) bool {
     if (builtin.os.tag == .wasi) {
         var statbuf: fdstat_t = undefined;
         const err = system.fd_fdstat_get(handle, &statbuf);
-        if (err != 0) {
+        if (err != .SUCCESS) {
             // errno = err;
             return false;
         }

lib/std/os/test.zig

@@ -1065,3 +1065,11 @@ test "timerfd" {
     try os.timerfd_settime(tfd, 0, &sit, null);
     try expectEqual(try os.poll(&fds, 5), 0);
 }
+
+test "isatty" {
+    var tmp = tmpDir(.{});
+    defer tmp.cleanup();
+
+    var file = try tmp.dir.createFile("foo", .{});
+    try expectEqual(os.isatty(file.handle), false);
+}