Prepare for NServiceBus 10 - Remove LangVersion (#1812)

* Remove LangVersion, as the language has been released

* Update Custom.Build.props

---------

Co-authored-by: particularbot6 <75360975+particularbot6@users.noreply.github.com>

Author: tamararivera

src/Custom.Build.props

@@ -1,9 +1,8 @@
-<Project>
+<Project>
 
   <PropertyGroup>
     <MinVerMinimumMajorMinor>9.0</MinVerMinimumMajorMinor>
     <MinVerAutoIncrement>minor</MinVerAutoIncrement>
-    <LangVersion>preview</LangVersion>
   </PropertyGroup>
 
   <!-- MSBuild tasks require a .NET Framework version to work in Visual Studo, so we have to multi-target. -->