Git dependencies can be inconsistent between compared runs

[Mark-Simulacrum]

e.g., https://crater-reports.s3.amazonaws.com/beta-1.46-1/1.45.2/gh/jockbert.jockbert_ants_bot/log.txt vs https://crater-reports.s3.amazonaws.com/beta-1.46-1/beta-2020-07-24/gh/jockbert.jockbert_ants_bot/log.txt shows:

https://github.com/jockbert/ants_ai_challenge_api#028d07e1
https://github.com/jockbert/ants_ai_challenge_api#1924a992

These two versions should be the same if we're to accurately reproduce ourselves.

[Mark-Simulacrum]

This is possible due to purging of caches and such on the gcp builders.

[Mark-Simulacrum]

This seems to still be the case, e.g., on the 1.52 beta run we had https://crater-reports.s3.amazonaws.com/beta-1.52-1/1.51.0/gh/jonlamb-gh.pinephone-rs-display-prototype/log.txt with embedded-layout at a different commit from https://crater-reports.s3.amazonaws.com/beta-1.52-1/beta-2021-03-27/gh/jonlamb-gh.pinephone-rs-display-prototype/log.txt, which caused a failure. It would be good to fix this - likely be sharing a Cargo.lock file between the two.