[gardening] Mark io/stdout_stderr_non_blocking_test flaky on x64

Issue: https://github.com/dart-lang/sdk/issues/35192
Change-Id: I6af9b935ba2fffbb32c854c36c3888df0258490d
Reviewed-on: https://dart-review.googlesource.com/c/90228
Auto-Submit: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Samir Jindel <sjindel@google.com>
Commit-Queue: Samir Jindel <sjindel@google.com>
diff --git a/tests/standalone_2/standalone_2_vm.status b/tests/standalone_2/standalone_2_vm.status
index fcd29ba..1880efc 100644
--- a/tests/standalone_2/standalone_2_vm.status
+++ b/tests/standalone_2/standalone_2_vm.status
@@ -90,7 +90,7 @@
 io/http_server_close_response_after_error_test: Pass, Timeout # Issue 28370: timeout.
 io/regress_7191_test: Pass, Timeout # Issue 28374: timeout.
 
-[ $runtime == dart_precompiled && $system == linux && ($arch == simarm || $arch == simarm64) ]
+[ $runtime == dart_precompiled && $system == linux && ($arch == simarm || $arch == simarm64 || $arch == x64) ]
 io/stdout_stderr_non_blocking_test: Pass, Timeout # Issue 35192
 
 [ $runtime == vm && !$checked && !$strong ]