Merge branch '382740-update-pipeline-docs' into 'master'

Update pipelines docs to clarify when full Jest jobs run

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/104796



Merged-by: Suzanne Selhorn <sselhorn@gitlab.com>
Approved-by: Jennifer Li <jli@gitlab.com>
Co-authored-by: Nao Hashizume <nhashizume@gitlab.com>