Skip mixin_export_test when using --use-sdk

pkg/pkg.status

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Don't run any test-like files that show up in packages directories. It
 # shouldn't be necessary to run "pub install" in these packages, but if you do
 # it shouldn't break the tests.
 */packages/*/*: Skip
 */*/packages/*/*: Skip
 */*/*/packages/*/*: Skip
@@ skipping 82 matching lines @@
 compiler/tool/generate_kernel_test*: Skip # Issue 28629
 front_end/test/src/incremental/hot_reload_e2e_test: Skip # Issue 28629
 
 [ $runtime == vm && ! $use_sdk ]
 front_end/tool/perf_test: Skip # Issue 28698
 
 [ $runtime == vm && $use_sdk ]
 front_end/tool/fasta_perf_test: SkipByDesign # depends on patched_sdk which is not built into the sdk
 front_end/test/kernel_generator_test: SkipByDesign # depends on patched_sdk which is not built into the sdk
 front_end/test/summary_generator_test: SkipByDesign # depends on patched_sdk which is not built into the sdk
+front_end/test/mixin_export_test: SkipByDesign # depends on patched_sdk which is not built into the sdk
 
 [ $runtime == vm && $system == windows]
 analysis_server/*: Skip # Issue 27557
 analysis_server/test/analysis/get_errors_test: Skip # runtime error, Issue 22180
 analysis_server/test/integration/analysis/analysis_options_test: RuntimeError # Issue 24796
 analyzer/test/generated/all_the_rest_test: Fail # Issue 21772
 analyzer/test/generated/source_factory_test: RuntimeError # Issue 26828
 kernel/test/baseline_spec_mode_test: RuntimeError # Issue 28243
 kernel/test/baseline_strong_mode_test: RuntimeError # Issue 28243
 analyzer/tool/task_dependency_graph/check_test: Slow, Pass
@@ skipping 111 matching lines @@
 analyzer_cli/test/driver_test: Pass, Slow, Timeout
 
 [ $runtime == vm && $system == windows ]
 analyzer/test/src/task/strong/checker_test: Pass, Slow
 
 [ $browser ]
 testing/test/analyze_test: SkipByDesign
 
 [ $browser || $runtime == flutter ]
 status_file/*: SkipByDesign # Only meant to run on the standalone VM.