Fixed RRF YAML REST Test: rrf with pinned retriever as a sub-retriever (elastic#130402)

* fixed failing pinned retriever test

* Update docs/changelog/130402.yaml

* Delete docs/changelog/130402.yaml

* Worked on the PR comments

* Fixed the Match_none

* space format

* space format
# Conflicts:
#	muted-tests.yml

Author: mridula-s109