Fix docs.rs build by avoiding --cfg docsrs in rustc flags

[paolobarbolini]

This should fix the docs.rs breakage for real. Reason: https://bsky.app/profile/paolobarbolini.bsky.social/post/3m2gqwacksc2g

# works
RUSTDOCFLAGS="--cfg docsrs" cargo doc --all-features --no-deps

# breaks
RUSTFLAGS="--cfg docsrs" RUSTDOCFLAGS="--cfg docsrs" cargo doc --all-features --no-deps

[weiznich]

Let's try this

[paolobarbolini]

It worked 🥳! Also, first time in a long time I see such a small build queue in docs.rs 😆