add .net5.0 targetframework in tests

tests/ImageSharp.Benchmarks/ImageSharp.Benchmarks.csproj

@@ -5,7 +5,7 @@
     <AssemblyName>ImageSharp.Benchmarks</AssemblyName>
     <OutputType>Exe</OutputType>
     <RootNamespace>SixLabors.ImageSharp.Benchmarks</RootNamespace>
-    <TargetFrameworks>netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>
+    <TargetFrameworks>net5.0;netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>
     <GenerateProgramFile>false</GenerateProgramFile>
     <!--Used to hide test project from dotnet test-->
     <IsTestProject>false</IsTestProject>

tests/ImageSharp.Tests.ProfilingSandbox/ImageSharp.Tests.ProfilingSandbox.csproj

@@ -8,7 +8,7 @@
     <Prefer32Bit>false</Prefer32Bit>
     <RootNamespace>SixLabors.ImageSharp.Tests.ProfilingSandbox</RootNamespace>
     <RuntimeIdentifier>win7-x64</RuntimeIdentifier>
-    <TargetFrameworks>netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>
+    <TargetFrameworks>net5.0;netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>
     <StartupObject>SixLabors.ImageSharp.Tests.ProfilingSandbox.Program</StartupObject>
     <!--Used to hide test project from dotnet test-->
     <IsTestProject>false</IsTestProject>

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -2,7 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>
+    <TargetFrameworks>net5.0;netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>
     <DebugSymbols>True</DebugSymbols>
     <AssemblyName>SixLabors.ImageSharp.Tests</AssemblyName>
     <Platforms>AnyCPU;x64;x86</Platforms>