Bump `ahash` to v0.7.8

[ribbanya]

Resolves a weird build regression with v0.7.6; more info in tkaitchuck/aHash#200.

❯ RUST_LOG=info cargo +nightly run --release -- nothoughts  
   Compiling ahash v0.7.6
error[E0635]: unknown feature `stdsimd`
  --> /home/user/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ahash-0.7.6/src/lib.rs:33:42
   |
33 | #![cfg_attr(feature = "stdsimd", feature(stdsimd))]
   |                                          ^^^^^^^