How to specify custom SPM snippets directory?

according to SE-356, it should be possible to specify a custom snippets directory with snippetsDirectory:

Similar to the ./Sources and ./Tests directories, a user may want to override the location of the ./Snippets directory with a new, optional snippetsDirectory argument to the Package initializer. Since snippet targets aren't declared individually in the manifest, the setting exists at the package level.

let package = Package(
    name: "MyPackage",
    snippetsDirectory: "Examples",
    products: [
      // ...
    dependencies: [
        // ...
    targets: [
        // ...

but when i try this, i get an error:

error: extra argument 'snippetsDirectory' in call
    snippetsDirectory: "Snippets",
error: ExitCode(rawValue: 1)

the manifest is using swift-tools-version:5.8 of course.