`--cap-lints=warn` is passed through via `RUSTFLAGS`, overriding `.cargo/config.toml`

[epage]

While #79 improves things so the users RUSTFLAGS are preserved,

• rustflags from .cargo/config.toml will be lost
• the user setting CARGO_ENCODED_RUSTFLAGS will cause --cap-lints=warn to be lost

See https://doc.rust-lang.org/cargo/reference/config.html#buildrustflags for the precedence order of the various RUSTFLAGS