ci: bsim workflow: Update bsim to version pointed by manifest

To ensure a reproducible enviroment while not needing
to update the docker images too often,
let's update on the fly the docker bsim installation to
whatever the Zephyr manifest points to.
Note that the update and rebuild is incremental,
so if the docker image already has the right version
the operation is very fast.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>