Bump C# language version to 14

Author: AArnott

Directory.Build.props

@@ -44,7 +44,7 @@
   </PropertyGroup>
 
   <PropertyGroup>
-    <LangVersion Condition="'$(MSBuildProjectExtension)'=='.csproj'">13</LangVersion>
+    <LangVersion Condition="'$(MSBuildProjectExtension)'=='.csproj'">14</LangVersion>
     <LangVersion Condition="'$(MSBuildProjectExtension)'=='.vbproj'">16.9</LangVersion>
   </PropertyGroup>