dogfood: unicode-normalization takes 3 minutes to check

[matthiaskrgr]

During the dogfood test ,clippy is run on itself to make sure its code has no clippy warnings.
During this process, clippy checks all the dependencies as well, however I think this may actually not be needed.

On my system, I can see that checking the unicode-normalization crate using clippy takes 2-3 minutes alone yet a simple "cargo check" of clippy seems to be much faster.

Perhaps we can somehow "cargo check" the dependencies in the dogfood test and only check the actual repo sourcecode using clippy for a decent dogfood speedup?

[flip1995]

Maybe this is also a problem, which will be solved with #3837.