invalid type: map, expected a string for key package.rust-version

[kkettinger]

When the key rust-version.workspace is used in the [package] group, i get this error:

error: failed to load manifest for workspace member `/home/devel/projects/slintui/slint/api/cpp`

Caused by:
  failed to parse manifest at `/home/devel/projects/slintui/slint/api/cpp/Cargo.toml`

Caused by:
  invalid type: map, expected a string for key `package.rust-version`

Contents of the Config.toml:

[package]
...
rust-version.workspace = true

[chrthi-work]

Possibly related: I get the same error for

edition.workspace = true
repository.workspace = true
license.workspace = true