Set `DisableImplicitNamespaceImports_Dotnet=true` to workaround sdk issue (#56744)

* Set `DisableImplicitNamespaceImports_Dotnet=true` to workaround sdk issue

* Disable just the imports declaration rather than the functionality

Directory.Build.props

@@ -287,7 +287,7 @@
     <ProduceReferenceAssembly>false</ProduceReferenceAssembly>
     <!-- We have very special projects that don't always contain default references. We also build MSBuild Tasks
     and there are some implicit namespaces that clash, i.e System.Threading.Tasks. -->
-    <DisableImplicitNamespaceImports>true</DisableImplicitNamespaceImports>
+    <DisableImplicitNamespaceImports_DotNet>true</DisableImplicitNamespaceImports_DotNet>
   </PropertyGroup>
 
   <PropertyGroup>