(maint) Remove reference assemblies

As we no longer target .NET Framework, we do not need to have a reference
for the .NET Reference Assemblies anymore. As such we remove these in this
commit.

Source/Cake.Codecov.Tests/Cake.Codecov.Tests.csproj

@@ -13,10 +13,6 @@
         </PackageReference>
         <PackageReference Include="FluentAssertions" Version="6.12.0" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.3" />
-        <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.2">
-            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
-            <PrivateAssets>all</PrivateAssets>
-        </PackageReference>
         <PackageReference Include="Moq" Version="4.16.1" />
         <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" />
         <PackageReference Include="xunit" Version="2.4.1" />

Source/Cake.Codecov/Cake.Codecov.csproj

@@ -38,10 +38,6 @@
         <PackageReference Include="Cake.Core" Version="2.0.0" PrivateAssets="All" />
         <PackageReference Include="CakeContrib.Guidelines" Version="1.4.0" PrivateAssets="All" />
         <PackageReference Include="JetBrains.Annotations" Version="2023.3.0" PrivateAssets="All" />
-        <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3">
-            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
-            <PrivateAssets>all</PrivateAssets>
-        </PackageReference>
         <PackageReference Include="Roslynator.Analyzers" Version="4.12.2">
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
             <PrivateAssets>all</PrivateAssets>