CI should build and run tests in both Debug and Release configurations

[eeberhard]

There's not much more than the title says. Right now the CI only builds and tests once in Debug configuration (when no configuration is specified in the cmake command, Debug configuration is default). Because optimisations in Release mode may introduce some unexpected changes, it is important to test in Release configuration as well.

I think I'll add a second workflow that does the exact same steps as the first, but instead builds and tests in Release configuration.

[eeberhard]

This idea was implented in PR #87. Closing the discussion thread.