OpenCppCoverage install step fails silently

> [Failed Run](https://github.com/microsoft/ebpf-for-windows/actions/runs/26356983057)
> [Codebase](https://github.com/microsoft/ebpf-for-windows/tree/cd22f202d18d1d689e17c62c571229e783b6303e)
> Test name - `unit_tests`
> Event - schedule
>

_Originally posted by @github-actions in [#5312](https://github.com/microsoft/ebpf-for-windows/issues/5312#issuecomment-4527962134)_

If the failure is transient, maybe adding a retry in this step would help.
Either way, if it cannot be installed, the step should fail, not succeed like it does now.

Start with the failed run and the referenced codebase commit, then locate the workflow step that installs OpenCppCoverage for the unit_tests test. Verify how installation failures are handled and whether a retry is appropriate; done means the step fails when installation fails and scheduled unit_tests runs no longer pass silently.

Written by the indexing model from the issue text.