Merge pull request #9766 from matrix-org/rav/drop_py35

.buildkite/scripts/test_old_deps.sh

changelog.d/9766.feature

scripts-dev/build_debian_packages

setup.py

synapse/storage/database.py

synapse/storage/databases/main/client_ips.py

synapse/storage/databases/main/devices.py

synapse/storage/databases/main/events_bg_updates.py

synapse/storage/engines/_base.py

synapse/storage/engines/postgres.py

synapse/storage/engines/sqlite.py

tests/storage/test_database.py

tox.ini