bug#47667: rust-rav1e-0.4 fails to build

[Leo Famulari]

While looking into upgrading the rav1e package, I noticed a new
rust-rav1e-0.4.0 package. However, it fails to build, like this:

------
starting phase `package'
   Packaging rav1e v0.4.0 (/tmp/guix-build-rust-rav1e-0.4.0.drv-0/rav1e-0.4.0)
error: failed to prepare local package for uploading

Caused by:
  no matching package named `assert_cmd` found
location searched: registry `https://github.com/rust-lang/crates.io-index`
required by package `rav1e v0.4.0 
(/tmp/guix-build-rust-rav1e-0.4.0.drv-0/rav1e-0.4.0)`
command "cargo" "package" "--no-metadata" "--no-verify" failed with status 101
builder for `/gnu/store/71dd3d1q50iwmqjab9528csp44k2nrh4-rust-rav1e-0.4.0.drv' 
failed with exit code 1
------

I checked the CI history:

https://ci.guix.gnu.org/search?query=rust-rav1e

The last successful build:

https://ci.guix.gnu.org/build/81950/details

The first failing build:

https://ci.guix.gnu.org/build/85107/details

By clicking the Evaluation number, you can learn the range of Git
commits that is different between these two builds. I took a look with
commands like this:

$ git log 
77f1bd9dea3def1992603cbf24c4b0003fa3e0f0^..e598556ee524a62544e777b1f0dd80316ef41754
 guix/build-system/cargo.scm

Maybe the build failure is fallout from 4d00185d6 (build-system/cargo:
Propagate crates across builds.)?