What does this implement/fix? Explain your changes.

Fixes #1359 by joining the traceback lines and separates the .NET stacktrace by an additional line.

Does this close any currently open issues?

#1359

Any other comments?

...

Checklist

Check all those that are applicable and complete.

• Make sure to include one or more tests for your change
• If an enhancement PR, please create docs and at best an example
• Add yourself to AUTHORS
• Updated the CHANGELOG