在我的项目中，我有两个特点：myfeatureA和myfeatureB。
我希望其中一个依赖于tokio，具有rt和sync特性，另一个依赖于tokio，仅具有sync特性。
我在Cargo.toml中尝试了这个配置：

[dependencies]
tokio = { version = "1.32", features = ["rt", "sync"], optional = true }

[features]
myfeatureA = ["dep:tokio"]
myfeatureB = ["dep:tokio/sync"]

$ cargo build --features=myfeatureB
error: failed to parse manifest at `[...]/myproject/Cargo.toml`

Caused by:
  feature `myfeatureB` includes `dep:tokio/sync` with both `dep:` and `/`
  To fix this, remove the `dep:` prefix.

所以，我删除了dep:前缀（这是这个other question提供的解决方案，但它不起作用）：

[features]
myfeatureA = ["dep:tokio"]
myfeatureB = ["tokio/sync"]

$ cargo build --features=myfeatureB
error: Package `myproject v0.1.0 ([...]/myproject)` does not have feature `tokio`. It has an optional dependency with that name, but that dependency uses the "dep:" syntax in the features table, so it does not have an implicit feature with that name.

如何使myfeatureB仅依赖于tokio的sync特性？