Failed to clone the index on CI

[pietroalbini]

We started seeing a lot of failures cloning the crates.io index across the rustc CI.

• Add Docker image to run AArch64 Linux tests #73650
  • Failure 1 (Azure)
  • Failure 2 (GHA)
• Use &raw in A|Rc::as_ptr #73845
  • Failure 1 (GHA)

[RalfJung]

More failures:

• Use exhaustive match in const_prop.rs #73693 (comment)
• Improve comments from #72617, as suggested by RalfJung #73925 (comment)

[oliviacrain]

Looks like this is still happening as of Oct 19 - #76688 has the same failure to clone the crates.io index on an 1686 platform.

Logs link for that run

This is a bit of a weird one- it seems like this issue is happening despite bootstrapping using the cargo beta from 2020-10-16, which includes the fix for this issue (rust-lang/cargo#8517).

[Enselic]

Triage: If this was still a problem I think this issue would not have gone silent? Closing as obsolete.