CI failures in MSRV jobs failing to pick up ahash version

[djc]

https://github.com/chronotope/chrono/actions/runs/6678120652/job/18148831947?pr=1343

Run cargo test --lib \
    Updating crates.io index
error: failed to select a version for the requirement `ahash = "^0.7.0"`
candidate versions found which didn't match: 0.4.8, 0.4.1, 0.4.0, ...
location searched: crates.io index
required by package `hashbrown v0.12.0`
    ... which satisfies dependency `hashbrown = "^0.12"` of package `rkyv v0.7.41`
    ... which satisfies dependency `rkyv = "^0.7.41"` of package `chrono v0.4.31 (/home/runner/work/chrono/chrono)`
Error: Process completed with exit code 101.

It's weird because ahash 0.7.7 was released 5 days ago but apparently isn't getting picked up here?