Python 2 is being used in tests but is now deprecated

Tests should be moved to python 3.

sam@memphis-wsl ~/work/gitlab/YDBOcto/build [master]341# rg -F '/usr/bin/env python' ..
../tests/fixtures/sqllogic/split_queries.py
1:#!/usr/bin/env python

../tests/fixtures/sqllogic/filter.py
1:#!/usr/bin/env python

../tests/fixtures/sqllogic/insert.py
1:#!/usr/bin/env python