Update dependency System.CodeDom to v7 (#43)

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

Author: renovate[bot]

IDLImporter/IDLImporter.csproj

@@ -14,7 +14,7 @@
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageReference Include="SIL.ReleaseTasks" Version="3.0.0" PrivateAssets="All" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
-    <PackageReference Include="System.CodeDom" Version="6.0.0" />
+    <PackageReference Include="System.CodeDom" Version="9.0.0" />
   </ItemGroup>
 
   <ItemGroup>