Accept header modified in request to service container

[michaelcaterisano]

I have a github action using the ubuntu-latest runner which runs an Apollo Router service container exposed on localhost:4001. I have a step that runs tests, which send http requests to Router at localhost:4001. The requests are making it, but Router is returning an error saying the Accept header has the incorrect value. I'm confident that the value is correct, and that other headers are making it to Router, because it returns different errors when I change other header values.

Is it possible that something related to the ubuntu-latest runner is modifying or removing the Accept header? Or perhaps docker's bridge network layer?