✨ Add nox task to verify dependency declarations

[ckunki]

Summary

pyproject.toml support different alternatives for declaring dependencies to other python packages:

• reference to a release published on pypi
• reference to a path in the local file system
• reference to a GitHub repository, optionally including a branch or commit SHA1

Details

The PTB should be enhanced

• to detect other references other than those to releases published on pypi
• avoid merging to the main branch

Background & Context

The Exasol Integration Team decided to only use references to releases published on pypi. Other references turned out to cause inconsistencies in dependencies and a lot of trouble.

Tasks

• [ ] add nox task
• [ ] enhance templates for GitHub workflows

[Jannis-Mittenzwei]

waiting for review by @Nicoretti