fix: library: ssl_tls12_client debug message

[arifbalik]

Description

Fixed a debug message log level. It was printing at error level which may confuse people who do debug

PR checklist

Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")

• [x] changelog provided, or not required
• [x] 3.6 backport done, or not required
• [x] 2.28 backport done, or not required
• [x] tests provided, or not required