cargo-fuzz's bundled Cargo.lock pinned rustix=0.36.5, which used the now-removed `rustc_attrs` cfg name and broke the install step on current nightly toolchain (the only toolchain that can build the fuzzers via libfuzzer-sys). Letting cargo resolve fresh picks a recent rustix that builds cleanly. Fixes the fuzz-smoke matrix on the v0.4.0 push CI run.