Always build Avalonia.Build.Tasks with netstandard2.0.

build/BuildTargets.targets

@@ -1,6 +1,6 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
-    <AvaloniaBuildTasksLocation>$(MSBuildThisFileDirectory)\..\src\Avalonia.Build.Tasks\bin\$(Configuration)\$(TargetFramework)\Avalonia.Build.Tasks.dll</AvaloniaBuildTasksLocation>
+    <AvaloniaBuildTasksLocation>$(MSBuildThisFileDirectory)\..\src\Avalonia.Build.Tasks\bin\$(Configuration)\netstandard2.0\Avalonia.Build.Tasks.dll</AvaloniaBuildTasksLocation>
     <AvaloniaUseExternalMSBuild>true</AvaloniaUseExternalMSBuild>
     <AvaloniaXamlIlVerifyIl>true</AvaloniaXamlIlVerifyIl>
   </PropertyGroup>

src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj

@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
         <TargetFrameworks>netstandard2.0</TargetFrameworks>
-        <TargetFrameworks Condition="$(Configuration) == 'Debug'">netstandard2.0;netcoreapp3.1;net6.0</TargetFrameworks>
         <OutputType>exe</OutputType>
         <GenerateDocumentationFile>false</GenerateDocumentationFile>
         <BuildOutputTargetFolder>tools</BuildOutputTargetFolder>