upgrade to System.CodeDom 6.0.0

Author: shuebner

XmlSchemaClassGenerator.SourceGenerator/XmlSchemaClassGenerator.SourceGenerator.csproj

@@ -34,7 +34,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="System.CodeDom" Version="5.0.0" PrivateAssets="all" GeneratePathProperty="true" />
+    <PackageReference Include="System.CodeDom" Version="6.0.0" PrivateAssets="all" GeneratePathProperty="true" />
     <PackageReference Include="System.Text.Encoding.CodePages" Version="5.0.0" PrivateAssets="all" GeneratePathProperty="true" />
     <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="5.0.0" PrivateAssets="all" GeneratePathProperty="true" />
     <PackageReference Include="System.ValueTuple" Version="4.5.0" PrivateAssets="all" GeneratePathProperty="true" />