[8.16] Fix BwC synonyms tests (#118691) (#118819)

* Fix BwC  synonyms tests (#118691)

(cherry picked from commit d09d57d)

# Conflicts:
#	muted-tests.yml
#	rest-api-spec/build.gradle
#	rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/synonyms/90_synonyms_reloading_for_synset.yml

* Fix merge

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Co-authored-by: Elastic Machine <[email protected]>

Author: carlosdelest