[CI] check for basop-ci-branch updates to work with BASOP float reference
- Requested reviewers: @norvell @pihlajakuja
For MRs to basop-ci-branch, clone the BASOP repo and build the ivas-float-update (reference) branch. Then run the long selftest to be sure that the changes do not break the reference in the BASOP repo (which happened a few times already).
One could think about protecting basop-ci-branch as well, so the only way of merging to it would be through MRs, but that would make small fixes more cumbersome and I would like to avoid that. This is more to have the opportunity of checking bigger changes, e.g. when merging in new testcases in self_test.py or so.