set LangVersion in all projects

Author: antonfirsov

Diff for: tests/ImageSharp.Benchmarks/ImageSharp.Benchmarks.csproj

@@ -11,7 +11,8 @@
     <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>-->
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <PropertyGroup>

Diff for: tests/ImageSharp.Tests.ProfilingSandbox/ImageSharp.Tests.ProfilingSandbox.csproj

@@ -14,6 +14,7 @@
     <EnsureNETCoreAppRuntime>false</EnsureNETCoreAppRuntime>
     <Configurations>Debug;Release</Configurations>
     <ValidateExecutableReferencesMatchSelfContained>false</ValidateExecutableReferencesMatchSelfContained>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <Choose>

Diff for: tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -7,6 +7,7 @@
     <Platforms>AnyCPU;x64;x86;ARM64</Platforms>
     <RootNamespace>SixLabors.ImageSharp.Tests</RootNamespace>
     <Configurations>Debug;Release</Configurations>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <Choose>