S3 repository: fix spelling error
S3 repository: fix spelling error

Reported at https://github.com/elastic/elasticsearch-cloud-aws/pull/221

Cherry-picked from bed9bf1

strapdata/elassandra-test,strapdata/elassandra-test,strapdata/elassandra-test,strapdata/elassandra-test,strapdata/elassandra-test,strapdata/elassandra-test,strapdata/elassandra-test