[Single Project MSIX] Generated appxsym/msixsym has Managed PDB when Native AOT is enabled

[dongle-the-gadget]

Describe the bug

Even with PublishAot=true in the project, Single Project MSIX produces a symbol file that contains Managed PDBs, not Native AOT PDBs.

Steps to reproduce the bug

1. Create a blank UWP .NET 9 application (or a blank Single Project MSIX WinUI 3 application)
2. In the csproj, make sure PublishAot is true.
3. Right click the project in Solution Explorer and go to Package and Publish > Create App Package
4. Make sure the shown dialog has "Sideloading" selected and go through the steps in the dialog.
5. Wait until build completes and open the package directory, see the presence of an appxsym or msixsym file.
6. Rename the appxsym/msixsym extension to zip and extract the PDB within.
7. Notice that the PDB file is only a few kilobytes large, which is too small for Native AOT PDBs.

Expected behavior

The PDB file within the symbol files generated should be a few megabytes at least.

Screenshots

No response

NuGet package version

Windows App SDK 1.7.1: 1.7.250401001

Packaging type

Packaged (MSIX)

Windows version

Insider Build (xxxxx)

IDE

Visual Studio 2022-preview

Additional context

This also occurs in Microsoft.Windows.SDK.BuildTools.MSIX version 1.7.20250508.1