Failing tests with `--all-features`

[TheLostLambda]

It looks like there is currently a test matrix that's testing the fancy and syntect-highlighter features as part of the CI, but out of curiosity I ran cargo test --all-features and found some tests that have been failing on main!

To prevent this from happening in the long-term, we could move away from the feature-matrix approach and use the --all-features flag in the CI, but looking at things more closely, it looks like this particular issue doesn't come from missing features, but from two features that are incompatible: cargo test --features fancy-no-syscall,fancy-no-backtrace causes the same errors.

Looking even closer, this is because those tests fail for fancy-no-syscall (if you force them to actually run — a module #cfg[...] means they don't by default). I don't know if it's intended that those tests shouldn't be run for that feature, but even with fancy-no-syscall, I do seem to get coloured output in my application? And the owo-colors dependency is being pulled in, so maybe this is something that just got missed?

It would be good to know if those tests are relevant, and if they are, then perhaps we could change the CI to use --all-features and catch these things early!