Treat (unmatched-skip) warnings as errors

[MarijnS95]

Is your feature request related to a problem? Please describe.

Whenever we remove a great deal of (transitive) crates, or upgrade our crate dependencies, there's a chance some (possibly duplicate) crate disappears while being specified in deny.toml. cargo-deny currently emits a useful warning for that such as warning[license-exception-not-encountered]: license exception was not encountered or warning[unmatched-skip]: skipped crate 'xxx = y.y.y' was not encountered. However, there's currently no way make cargo-deny fail in our CI to complain about this overspecification, as we can now finally drop some skip/exception from our deny.toml.

Describe the solution you'd like
Treating these warnings as errors, so that our CI fails until the now-unused skip declaration has been removed.

Describe alternatives you've considered
None.

Additional context
None.

[Jake-Shadle]

Use -D, --deny <lint_names> https://embarkstudios.github.io/cargo-deny/cli/check.html#-d---deny-deny

[MarijnS95]

@Jake-Shadle Ah perfect, thanks! Looks like -D warnings catches all warnings, that's amazing!

Didn't know it was a config option on check rather than on cargo deny (just like how --workspace has to be passed before check, since it's a subcommand).

[Jake-Shadle]

Other commands don't have diagnostics, only check.