Bump Microsoft.UI.Xaml from 2.8.0-prerelease.220712001 to 2.8.0 (#9581)

Bumps [Microsoft.UI.Xaml](https://github.com/microsoft/microsoft-ui-xaml) from 2.8.0-prerelease.220712001 to 2.8.0.
- [Release notes](https://github.com/microsoft/microsoft-ui-xaml/releases)
- [Commits](microsoft/microsoft-ui-xaml@v2.8.0-prerelease.220712001...v2.8.0)

---
updated-dependencies:
- dependency-name: Microsoft.UI.Xaml
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]

src/Files.Uwp/Files.Uwp.csproj

@@ -1586,7 +1586,7 @@
       <Version>7.1.2</Version>
     </PackageReference>
     <PackageReference Include="Microsoft.UI.Xaml">
-      <Version>2.8.0-prerelease.220712001</Version>
+      <Version>2.8.0</Version>
     </PackageReference>
     <PackageReference Include="Microsoft.Xaml.Behaviors.Uwp.Managed">
       <Version>2.0.1</Version>