gcc jobs: lalburst cannot import name 'pipeline' from 'glue'

This is the newest CI failure, affecting ~~most of~~ the gcc 9+10+11 compiler test jobs + coverage (which apparently uses gcc8). Clang and gcc7 are unaffected, as are the dedicated lalburst jobs. See e.g. https://git.ligo.org/lscsoft/lalsuite/-/pipelines/589860 on master.