Update TargetFrameworks in Avalonia.Vulkan.csproj (#15578)

Author: kekekeks

src/Avalonia.Vulkan/Avalonia.Vulkan.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
+        <TargetFrameworks>$(AvsCurrentTargetFramework);$(AvsLegacyTargetFrameworks);netstandard2.0</TargetFrameworks>
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     </PropertyGroup>