Cannot handle projects from Xcode 16.3

The Xcode 16.3 project structure changes the shellScript of a build phase to an Array instead of string. Sample diff

```diff
- shellScript = "sh ../../scripts/swiftlint.sh\n";
+ shellScript = (
+ "sh ../../scripts/swiftlint.sh",
+ "",
+ );
```

This results in the error: **[Xcodeproj] Type checking error: got `Array` for attribute: attribute 'shellScript' (type: `simple`, classes: `[String]`, owner class : `PBXShellScriptBuildPhase`**

I haven't found any project-specific conditionals for declarations so I'm unsure what's the best (backwards compatible) way to solve this but the relevant line is [here](https://github.com/CocoaPods/Xcodeproj/blob/ab3dfa504b5a97cae3a653a8924f4616dcaa062e/lib/xcodeproj/project/object/build_phase.rb#L328).

Can someone point me in the right direction how I could fix this then I'd open a PR.