Support sub-nanosecond precision on Cargo benchmarks

In https://github.com/rust-lang/rust/pull/124774, Rust changed the output of benchmarks to contain sub-nanosecond precision. This was first published in `nightly-2024-05-11` which started breaking CI that used github-action-benchmark since it couldn't find any benchmarks in an output file.

https://github.com/benchmark-action/github-action-benchmark/pull/243#issue-2292982944