Enable testing for NAG compiler

What is the new feature

Enable testing for NAG compiler. This MR closes #10 (closed) and #12 (closed)

How is it implemented

This includes fixing FortUTF to work with NAG compiler.

• PR fix for FortUTF https://github.com/artemis-beta/FortUTF/pull/21

Mandatory steps before review

• Gitlab CI passes (Hint: use make format for linting)
• New feature is covered by additional unit tests
• Mark the merge request as ready by removing Draft:

Mandatory steps before merge

• Reviewed by a maintainer
• Incorporate review suggestions
• Remember to edit the commit message and select the proper changelog category (feature/bugfix/other)

You are not supposed to merge this request by yourself, the maintainers of fortan-support take care of this action!