"/MR-604-nginx-default.conf": not found

With eclipsefdn/it/websites/membership.eclipse.org!604 (merged), I am trying to use our preview framework to simply deploy previews of the front-end stack without the API.

However, it's failing with the following error:

#6 [2/3] COPY MR-604-nginx-default.conf /etc/nginx/conf.d/default.conf
#6 ERROR: failed to calculate checksum of ref x15cs2jztg60xj4wge6h6plnl::rkl7cj4hi3qtruoj3wpki5oda: "/MR-604-nginx-default.conf": not found
------
 > [2/3] COPY MR-604-nginx-default.conf /etc/nginx/conf.d/default.conf:

I am not specifying a custom Nginx file. I would expect this to copy https://gitlab.eclipse.org/eclipsefdn/it/releng/jenkins-pipeline-library/-/blob/main/resources/org/eclipsefdn/jamstack/nginx/default.conf

/cc @mbarbero @heurtemattes