Merge pull request #2896 from SixLabors/af/fix-3.1-build

[3.1] Set LangVersion=12 unconditionally

Author: JimBobSquarePants

Directory.Build.props

@@ -21,9 +21,9 @@
   <!-- Import the shared global .props file -->
   <Import Project="$(MSBuildThisFileDirectory)shared-infrastructure\msbuild\props\SixLabors.Global.props" />
 
-  <PropertyGroup Condition="$(SIXLABORS_TESTING_PREVIEW) == true">
+  <PropertyGroup>
     <!-- Workaround various issues bound to implicit language features. -->
-    <LangVersion>preview</LangVersion>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <!--

tests/ImageSharp.Benchmarks/ImageSharp.Benchmarks.csproj

@@ -11,7 +11,7 @@
     <IsTestProject>false</IsTestProject>
     <Configurations>Debug;Release</Configurations>
     <!-- Uncomment this to run benchmarks depending on Colorful or Pfim (colorspaces and TGA): -->
-    <!--<SignAssembly>false</SignAssembly>-->    
+    <!--<SignAssembly>false</SignAssembly>-->
   </PropertyGroup>
 
   <PropertyGroup>