fix(wf-bss2-demos): disable full notebook execution at installtest time

There is some instability ("stuck tests", maybe also non-deterministic fails?) in the notebooks run at install time — we don't want that. → Disable for now, and wait for the cronjob-like health checker/tester. (We might readd some local-only tests that verify the environment but don't interact with external things like the BSS-2 experiment service.)