maturin upload in the generated CI flow does not appear to work wth testpypi when using -r testpypi as an argument

I generated the CI file using 1.86 maturin and tried to use the upload -r argument to set it to testpypi rather than pypi but it seems to ignore it in the action. 

I could get it to work by using env instead.
MATURIN_REPOSITORY: testpypi

I'm not sure if this is an oversight or intended behaviour.