Update Microsoft.AspNetCore.Mvc.Testing requirement from 6.0.* to 7.0.*

Updates the requirements on [Microsoft.AspNetCore.Mvc.Testing](https://github.com/dotnet/aspnetcore) to permit the latest version.
- [Release notes](https://github.com/dotnet/aspnetcore/releases)
- [Changelog](https://github.com/dotnet/aspnetcore/blob/main/docs/ReleasePlanning.md)
- [Commits](dotnet/aspnetcore@v6.0.0...v7.0.13)

---
updated-dependencies:
- dependency-name: Microsoft.AspNetCore.Mvc.Testing
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Directory.Build.props

@@ -22,7 +22,7 @@
     <CodeAnalysisFrozenVersion>4.1.0</CodeAnalysisFrozenVersion>
 
     <!-- Non-published dependencies (these are safe to update, won't cause a breaking change) -->
-    <AspNetCoreVersion>6.0.*</AspNetCoreVersion>
+    <AspNetCoreVersion>7.0.*</AspNetCoreVersion>
     <BogusVersion>34.0.*</BogusVersion>
     <CSharpGuidelinesAnalyzerVersion>3.8.*</CSharpGuidelinesAnalyzerVersion>
     <CoverletVersion>6.0.*</CoverletVersion>