Backporting prepared

Author: stesee

.github/workflows/dotnet.yml

@@ -1,6 +1,6 @@
 name: .NET build and test
 env:
-  CURRENT_VERSION: 3.0.${{ github.run_number }}
+  CURRENT_VERSION: 2.0.${{ github.run_number }}
   LAST_COMMIT_MESSAGE: ${{ github.event.head_commit.message }}
 
 on:

ImageSharpCompare/ImageSharpCompare.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
 	<PropertyGroup>
-		<TargetFramework>net6.0</TargetFramework>
+		<TargetFramework>netstandard2.0</TargetFramework>
 		<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 		<GenerateDocumentationFile>true</GenerateDocumentationFile>
 		<RepositoryUrl>https://github.com/Codeuctivity/ImageSharp.Compare</RepositoryUrl>
@@ -43,7 +43,7 @@
 	</ItemGroup>
 
 	<ItemGroup>
-		<PackageReference Include="SixLabors.ImageSharp" Version="3.0.1" />
+		<PackageReference Include="SixLabors.ImageSharp" Version="2.1.4" />
 		<PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="all" />
 		<PackageReference Include="SonarAnalyzer.CSharp" Version="8.49.0.57237">
 			<PrivateAssets>all</PrivateAssets>

ImageSharpCompareTestNunit/ImageSharpCompareTestNunit.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
 	<PropertyGroup>
-		<TargetFramework>net6.0</TargetFramework>
+		<TargetFrameworks Condition="'$(OS)' == 'Windows_NT' ">net48;net6.0</TargetFrameworks>
+		<TargetFrameworks Condition="'$(OS)' != 'Windows_NT' ">net6.0</TargetFrameworks>
 		<IsPackable>false</IsPackable>
 		<LangVersion>8.0</LangVersion>
 		<Nullable>enable</Nullable>