Creating a package with .snupkg symbols fails with error NU5005

Repro steps

1. Create the following project:

<?xml version="1.0" encoding="utf-8"?>
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
    <IncludeSymbols>true</IncludeSymbols>
    <SymbolPackageFormat>snupkg</SymbolPackageFormat>
  </PropertyGroup>
  <Import Project=".paket\Paket.Restore.targets" />
</Project>

2. paket convert-from-nuget.

3. dotnet pack

Expected behavior

A .snupkg file would be created alongside with its main .nupkg package file.

Actual behavior

C:\Users\teots\code\paket-bug\.paket\Paket.Restore.targets(304,5): error NU5005: Failed to build package. Ensure 'C:\Users\teots\code\paket-bug\obj\Debug\paket-bug.1.0.0.nuspec' includes source and symbol files. For help on building symbols package, visit https://docs.nuget.org/. [C:\Users\teots\code\paket-bug\paket-bug.csproj]

Additional information

I saw a paket-bug.1.0.0.symbols.nuspec file inside obj/Debug. Was Paket trying to create a legacy .symbols.nupkg file? Maybe my previous fix in #3636 was not enough.

Reproduce the issue with the shown project, paket convert-from-nuget, and dotnet pack. Start at .paket/Paket.Restore.targets around line 304 and inspect the generated obj/Debug nuspec files, including the .symbols.nuspec. Done means dotnet pack creates the expected .snupkg alongside the main .nupkg without NU5005.