Add a command to run retired tests

[RLThomaz]

There are commands to run all or a selected test, and with the advent of retired tests, we would benefit from a command to run only retired tests.

My use case is a header-only library that only triggers the rebuild of unit tests affected by changes. Those unit tests are then automatically set as retired by this extension. However, running all tests will actually run them all - even untouched ones.