Attempt to include C++ 'exercises' into CI

[kylecordes]

The C++ code had some helpful pre-existing commands that we can use to validate in CI things actually work.

Currently, one of them does not work. A problem to be solved.

[kylecordes]

This quick initial change is just to get the problem in front of Alex. I did not jump through the hoops to pass the CI-specific .bazelrc settings all the way through yet.

[aspect-workflows]

Test

All tests were cache hits

22 tests (100.0%) were fully cached saving 5s.

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Lint

[alexeagle]

LMK when this is ready, removing from my review dashboard

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