FluentAssertions package is not Authenticode signed

### Description

FluentAssertions package is not Authenticode signed

### Complete minimal example reproducing the issue

Our compliance requirement to use this package to prevent supply-chain attacks is that it is Strong Name and Authenticode signed. StrongName proves it was not tampered, and Authenticode proves who produced the binary.

### Actual behavior:
FluentAssertions binaries are StrongName signed but not authenticode signed.

```
sn.exe -vf "...\fluentassertions.5.6.0.nupkg\lib\net45\FluentAssertions.dll"
Microsoft (R) .NET Framework Strong Name Utility Version 4.0.30319.0
Copyright (c) Microsoft Corporation. All rights reserved.

Assembly '...\fluentassertions.5.6.0.nupkg\lib\net45\FluentAssertions.dll' is valid
```

However it is not authenticode signed.
`chktrust -v `
pops a dialog saying the publisher cannot be verified. Can also right click the binary and check signature to see there is none.

### Versions

* Which version of Fluent Assertions are you using?
5.6.0
* Which .NET runtime and version are you targeting? E.g. .NET framework 4.6.1 or .NET Core 2.0.
All