Use a private tangle in CI

[eike-hass]

Description of change

Please write a summary of your changes and why you made them.

Links to any relevant issues

Be sure to reference any related issues by adding fixes issue #.

Type of change

Add an x to the boxes that are relevant to your changes.

• [ ] Bug fix (a non-breaking change which fixes an issue)
• [X] Enhancement (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Fix

How the change has been tested

The changes can only be tested in CI.

Change checklist

Add an x to the boxes that are relevant to your changes.

• [ ] I have followed the contribution guidelines for this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes