Fix missing python includes for Unix hosts

[UebelAndre]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

This PR fixes the current breakage on some platforms when building packages from sdist artifacts.

This change is an extension of #803 but applies part of the change to MacOS hosts to Linux hosts as well.

Issue Number:

• Includes fix: Add python include for compilation #803 (Thank you @illicitonion!)

What is the new behavior?

Adds the correct import path to be able to find Python.h

Does this PR introduce a breaking change?

• Yes
• No

Other information

[groodt]

LGTM