[3.13] gh-142352: Fix asyncio start_tls() to transfer buffered data from StreamReader (GH-142354) (#145364)

[3.13] gh-142352: Fix `asyncio` `start_tls()` to transfer buffered data from StreamReader (GH-142354)
(cherry picked from commit 0598f4a8999b96409e0a2bf9c480afc76a876860)

Co-authored-by: Maksym Kasimov <39828623+kasimov-maxim@users.noreply.github.com>