The pre-commit hook does not work because `deadcode`'s exit code is 0 even when issues are found

As stated in the pre-commit [docs](https://pre-commit.com/#new-hooks:~:text=The%20hook%20must%20exit%20nonzero%20on%20failure%20or%20modify%20files.):

> The hook must exit nonzero on failure or modify files.