Unable to check for yanked crates when crates.io git registry is outdated

[jplatte]

Describe the bug

When the git-based crates.io registry is outdated or missing, cargo deny fails to check for yanked crates, with a mediocre error message:

warning[index-failure]: unable to check for yanked crates
  ┌─ /home/jplatte/code/ruma/.deny.toml:1:1
  │
1 │ # https://embarkstudios.github.io/cargo-deny/checks/cfg.html
  │ ^ lint level defined here
  │
  = failed to find crate in git index

To Reproduce

• Delete ~/.cargo/registry

• (May not be needed) Add the following to ~/.cargo/config.toml

  [registries.crates-io]
  protocol = "sparse"

• Run cargo deny check in some project

Expected behavior

Yanked crates should still be checked ideally :)