Fix BwC synonyms tests (elastic#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

Author: carlosdelest