Using ✅ ❌ in `Fallow vs linters` will improve readability

[2u841r]

maybe for slow sloth (🦥), snail (🐌), and turtle (🐢), ⏳

site: https://docs.fallow.tools/explanations/fallow-vs-linters#what-each-tool-finds
file: https://github.com/fallow-rs/docs/blob/main/explanations/fallow-vs-linters.mdx