fix(ci): run build as test
This allows for a build to be a sufficient test criterion for auto-merging. The convention for the tested job is to be in the test stage and called test.
It still allows to reuse the artifact from the test build to be deployed as a review app, now called test app.
The manifest for a test build is also reused by the independent pages pipeline.
Removing the additional test step after building halves CI time from 4' to 2'.
addresses #41 (closed)