Fix issue with nested script strings in CI reproduce script
The reproduce_ci_env.py
script reads in the yaml for the GitLab
runners and replicates the runs using Docker. Through a quirk of the
implemenation of MR !3191 (merged), some of the scripts, which are expected to be
a list of command strings, get defined as a list of lists. This is fixed
by flattening this list of commands.