Corrected target frameworks.

Author: dlemstra

src/Magick.NET.AvaloniaMediaImaging/Magick.NET.AvaloniaMediaImaging.csproj

@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net8.0;net462</TargetFrameworks>
-    <TargetPlatformIdentifier>Windows</TargetPlatformIdentifier>
+    <TargetFrameworks>net8.0;netstandard20</TargetFrameworks>
     <Platforms>AnyCPU</Platforms>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <FileVersion>1.0.0</FileVersion>