Lint if ignore_run_exports is in wrong section (under requirements, instead of build)

[corneliusroemer]

The docs aren't super clear where to put ignore_run_exports, so it can happen they are in the wrong place (under requirements instead of build).

I made this mistake here: bioconda/bioconda-recipes@31c6842#diff-1f143fe375ca4f6a95329eb32f79d7f8b9810e63d6f9ef937eec75fecba98c2eL31-L33

And someone else here: https://github.com/bioconda/bioconda-recipes/blob/74934d5f8a3c9b84a050c733eecfafa833511583/recipes/libmaus2/meta.yaml#L42

Might be nice to add a lint for it.