Bump Microsoft.Toolkit.Mvvm from 7.0.0-preview3 to 7.0.0-preview4 (#2326)

Bumps [Microsoft.Toolkit.Mvvm](https://github.com/windows-toolkit/WindowsCommunityToolkit) from 7.0.0-preview3 to 7.0.0-preview4.
- [Release notes](https://github.com/windows-toolkit/WindowsCommunityToolkit/releases)
- [Commits](https://github.com/windows-toolkit/WindowsCommunityToolkit/commits/v7.0.0-preview4)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Files/Files.csproj

@@ -673,7 +673,7 @@
       <Version>6.2.10</Version>
     </PackageReference>
     <PackageReference Include="Microsoft.Toolkit.Mvvm">
-      <Version>7.0.0-preview3</Version>
+      <Version>7.0.0-preview4</Version>
     </PackageReference>
     <PackageReference Include="Microsoft.Toolkit.Uwp">
       <Version>6.1.1</Version>