Update dependency DotNext to 5.21.0 (#1045)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

src/Directory.Packages.props

@@ -787,7 +787,7 @@
 		<PackageVersion Include="CommunityToolkit.HighPerformance" Version="8.4.0">
 		</PackageVersion>
 		<!-- 👇 DotNext（一组功能强大的库，旨在提高开发效率并扩展具有独特功能的 .NET API） -->
-		<PackageVersion Include="DotNext" Version="5.18.0">
+		<PackageVersion Include="DotNext" Version="5.21.0">
 		</PackageVersion>
 		<PackageVersion Include="DotNext.Threading" Version="5.18.1">
 		</PackageVersion>