Merge branch 'ld-docs-idempotent-worker-prefer-it_behaves_like' into 'master'

Docs for 'an idempotent worker' to use `it_behaves_like`

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/136011



Merged-by: Jessie Young <jessieyoung@gitlab.com>
Approved-by: Jessie Young <jessieyoung@gitlab.com>
Co-authored-by: Luke Duncalfe <lduncalfe@eml.cc>