I fancy it only wont start as a systemd upstart job, I'm using Ubuntu server and have the same issue because Ubuntu's installation of redis-server does not use redis's ability to communicate with systemd. On this platform you should leave redis.conf set as it shipped. Most likely this would work

./redis-server --tls-port 6379 --port 0 \
--tls-cert-file ./tests/tls/redis.crt \
--tls-key-file ./tests/tls/redis.key \
--tls-ca-cert-file ./tests/tls/ca.crt