Package.swift is not used with Swift 5.9.1

As already metioned [here](https://github.com/compnerd/swift-win32/issues/768#issuecomment-1783894205) I can not build this repo with Swift 5.9.1. I get the following error when I type `swift build --product UICatalog`.

```cmd
error: 'swift-win32': package 'package@swift-5.9.swift' is using Swift tools version 3.1.0 which is no longer supported; consider using '// swift-tools-version: 5.9' to specify the current tools version
```

I was only able to fix it by copy `Package@swift-5.4.swift` to `Package@swift-5.9.swift` and change the swift-tools-version to 5.9.

`Package.swift` should be chosen by swift and the swift-tools-version 5.7.0 there should be fine when working correctly as @compnerd [mentioned](https://github.com/compnerd/swift-win32/issues/768#issuecomment-1783898506).

Start by comparing Package.swift and Package@swift-5.4.swift, then reproduce the issue with `swift build --product UICatalog` using Swift 5.9.1. Check how Swift selects the package manifest and verify that the build no longer treats the selected manifest as using Swift tools version 3.1.0.

Written by the indexing model from the issue text.