ZTS: Fix zfs_load-key failures on F39

The zfs_load-key tests were failing on F39 due to their use of the
deprecated ssl.wrap_socket function. This commit updates the test to
instead use ssl.SSLContext() as described in
https://stackoverflow.com/a/65194957.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #15534
Closes #15550