Update status for front_end/test/mixin_export_test

pkg/pkg.status

Index: pkg/pkg.status
diff --git a/pkg/pkg.status b/pkg/pkg.status
index 9ccead13d22d16f356b776a283b3aaa41aa8ed92..a868cfbdb69fecf4f7ed896b734970274a8a08ae 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -138,6 +138,9 @@ front_end/test/src/base/libraries_reader_test: SkipByDesign # Uses dart:io
 front_end/test/src/base/processed_options_test: SkipByDesign # Uses dart:io
 front_end/test/subpackage_relationships_test: SkipByDesign # Uses dart:io
 
+[ $compiler == dart2js && $runtime != d8 ]
+front_end/test/mixin_export_test: RuntimeError # Issue 30576
+
 [ $compiler == dart2js && $fast_startup ]
 front_end/test/*: SkipByDesign # Tests written with dart:mirrors.