Windows CI does not fail if one or more tests fail

While I was working on updating the Windows CI, I noticed that some tests were failing, but the test suite -- and the GitHub Actions workflow as a whole -- succeeded anyway. We should probably change that.

Start by inspecting the GitHub Actions workflow for the Windows CI and how it runs the C++ test suite. Reproduce or review the case where tests fail while the workflow succeeds, then verify that any failing test causes the Windows job and overall workflow to fail.

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