recommended use "ssl://" transport.

in php 5.5 ~ 7.1
ssl:// transport = ssl_v2|ssl_v3|tls_v1.0|tls_v1.1|tls_v1.2
tls:// transport = tls_v1.0

after 7.2 ssl:// and tls:// transports is same
php 7.2 ~ 7.3 = tls_v1.0|tls_v1.1|tls_v1.2
php 7.4 ~ 8.1 = tls_v1.0|tls_v1.1|tls_v1.2|tls_v1.3