Lower the lint level of `manual_readme` and `non_kebab_case_bins` to `allow` (#17478)

After some discussion in today's Cargo team meeting ([summary
here](https://github.com/rust-lang/cargo/issues/17461#issuecomment-5683349002)),
it was decided that it would be best to temporarily lower the lint level
of `manual_readme` and `non_kebab_case_bins` to `allow`. This PR makes
that change by moving both lints to the `pedantic` group for the time
being.

Fixes #17461