If there are no version packaging should fails instead of generating version 1.0.0

[MangelMaxime]

Is your feature request related to a problem? Please describe.

If you have the following changelog:

# Changelog
All notable changes to this project will be documented in this file.

The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

## Unreleased

* Item 1
* Item 2

Running dotnet pack should fails and not "Successfully create package [...]/bin/Release/Thoth.Json.Core.1.0.0.nupkg'"