Adapt tests for qualified paths for Windows

[cderv]

Qualified paths were added in #2429

• https://github.com/quarto-dev/quarto-cli/blob/main/src/core/qualified-path.ts

Currently, tests are not made for windows: https://github.com/quarto-dev/quarto-cli/blob/main/tests/unit/paths/qualified-path.test.ts

In #4099, I'll ignore tests for now until this is fixed.

[cscheid]

(Let's close this one and reopen when we actually have started using QualifiedPath consistently in the code)