Auto retry on checksum verification

[schneems]

This error is failing integration tests in #51 twice and once in #47 right now. Retrying it fixes the issue, but it seems like we could make it more robust by auto-retrying a few times before failing the build:

! Package Index checksum verification failed
!
! While updating package sources, an error occurred while verifying the checksum of the Package Index at http://ports.ubuntu.com/ubuntu-ports/dists/noble-security/universe/binary-arm64/by-hash/SHA256/31cee22670a31bc8e716d355bd8b018a5110779f1274f7611432d8165e127a15. This error can occur due to an issue with the upstream Debian package repository.
!
! Checksum:
! - Expected: `31cee22670a31bc8e716d355bd8b018a5110779f1274f7611432d8165e127a15`
! - Actual: `1c014851f67940f5bcd06bf3db4976f7eed3e7ddb0377d18d20e96efe608e940`
!
! Use the debug information above to troubleshoot and retry your build.

ERROR: failed to build: exit status 1


note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Possibly there's something else we could do to harden the download and check process.

[colincasey]

I've noticed this too. The instability has become more pronounced recently and it seems to happen specifically around this checksum on the Heroku-24 / arm64 variant. I want to do a bit more investigating around the "why" before jumping straight into a fix but I was thinking along the lines of an auto-retry as well.