Bump Microsoft.AspNetCore.All from 2.1.4 to 2.1.21

Bumps [Microsoft.AspNetCore.All](https://github.com/aspnet/AspNetCore) from 2.1.4 to 2.1.21.
- [Release notes](https://github.com/aspnet/AspNetCore/releases)
- [Changelog](https://github.com/dotnet/aspnetcore/blob/main/docs/ReleasePlanning.md)
- [Commits](https://github.com/aspnet/AspNetCore/compare/2.1.4...v2.1.21)

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

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

samplebrowser.csproj

@@ -10,7 +10,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.ApplicationInsights.AspNetCore" Version="2.1.1" />
-    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.1.4" />
+    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.1.21" />
     <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.1.1" />
     <PackageReference Include="Microsoft.Extensions.Logging.Debug" Version="2.1.1" />
     <PackageReference Include="Microsoft.VisualStudio.Web.BrowserLink" Version="2.1.1" />