Fails if Cargo.lock or Cargo.toml are read-only

[sendittothenewts]

To wit:

$ chmod -w Cargo.lock; cargo outdated
error: failed to write /tmp/cargo-outdatedv46WLk/Cargo.lock

Caused by:
  failed to open: /tmp/cargo-outdatedv46WLk/Cargo.lock

Caused by:
  Permission denied (os error 13)
$ chmod -w Cargo.toml; cargo outdated
error: Permission denied (os error 13)

The error message is particularly uninformative when Cargo.toml is read-only.

This issue also occurs in workspaces if any of the members' Cargo.toml is read-only.