Disable flaky lldb-vscode tests on aarch64

Summary:
These two tests are flaky only on this arch for some reason. They are testing important features and are not flaky on x86_64, so I'll investigate this arm issue separatedly.

Some flaky runs:
http://lab.llvm.org:8011/builders/lldb-aarch64-ubuntu/builds/5517/steps/test/logs/stdio
http://lab.llvm.org:8011/builders/lldb-aarch64-ubuntu/builds/5527/steps/test/logs/stdio

Diff that created those tests:
https://reviews.llvm.org/D81978