Run the local version of `wasp-app-runner` instead of the published one

[cprecioso]

When working on #3159, it needed some fixes in the Wasp App Runner. I had to extract those changes to another PR (at #3168), because the headless tests for each example app install wasp-app-runner from npm, instead of using the one inside the repo. If I want the CI tests to go green, I need to extract the PR, publish, and then update the headless tests to use the new version.

It would be most comfortable if the headless tests used the wasp-app-runner of the current tree, so that changes can be made in sync, and a publish is not needed for an in-progress PR.

[cprecioso]

Putting this on the backlog right away as it should not be very often that we run against this problem, so investing time in this might not make sense right away.

[cprecioso]

The dance of having to build wasp-app-runner before running the e2e tests could be eased with something like #3170