Fix header check is always true (!67)

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## What is the bug
The header check macros are always true
## How do you fix it
Make it configured to the same as the CMake variable, where the presence of the header is checked.

## How urgent is the bugfix
- [ ] I need it as soon as possible
- [x] I can wait for a couple of days
- [ ] None of my current codes is directly affected

## Mandatory steps before review
- [x] Gitlab CI passes _(Hint: use `make format` for linting)_ 
- [x] Bugfix is covered by additional unit tests
- [x] Mark the merge request as ready by removing `Draft:`

## Mandatory steps before merge
- [x] Test coverage does not decrease
- [ ] 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!**

Approved-by: Jonas Jucker <jonas.jucker@env.ethz.ch>
Merged-by: Jonas Jucker <jonas.jucker@env.ethz.ch>
Changelog: bugfix