Update dependency DotNext.Threading to 5.21.0 (#1046)

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

Author: renovate[bot]

src/Directory.Packages.props

@@ -789,7 +789,7 @@
 		<!-- 👇 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="5.21.0">
 		</PackageVersion>
-		<PackageVersion Include="DotNext.Threading" Version="5.18.1">
+		<PackageVersion Include="DotNext.Threading" Version="5.21.0">
 		</PackageVersion>
 	</ItemGroup>
 	<!-- 👇 Composition（组件扩展业务插件） -->