How to set RUSTFLAGS in release.yml?

I need to set
`rustflags = ["--cfg", "tokio_unstable"]`

or `export RUSTFLAGS="--cfg tokio_unstable"`

as part of my build, but can't figure out how to get release.yml to pick it up. When I modify the release.yml generated by cargo-dist to set RUSTFLAGS inline whenever it runs build I get an error that the release.yml is dirty as part of `plan`.

What's the correct way to set build flags for cargo-dist as part of CI?

Start by reading how cargo-dist generates release.yml and how plan detects a dirty generated workflow. Trace where build commands are configured and where RUSTFLAGS could be supplied without editing the generated file. Done means the supported CI configuration is documented or identified and plan no longer reports release.yml as dirty.

Written by the indexing model from the issue text.