Some statements are always replicated in STATEMENT binlog format.
So upon their execution, the current binlog format is temporarily
switched to STATEMENT even though the session's format is different.
This state, stored in THD's current_stmt_binlog_format, was getting
incorrectly masked by wsrep_forced_binlog_format, causing assertions
and unintended generation of row events.

Backported galera.galera_forced_binlog_format and added a test
specific to this case.