gitlab-ci: `fdroid build` uses --test to keep APKs that fail reproducing
To aide reproducible builds debugging, this makes the fdroid build
job keep the unsigned APK that was built even when the verification fails. There is a test run here:
https://gitlab.com/eighthave/fdroiddata/-/jobs/1178431810
This can be merged now, but will only fully take effect once fdroidserver!904 (merged) is merged.
Edited by Hans-Christoph Steiner