setup: bump sqlalchemy minimum version to 1.2.9 to get rid of py3 warning

Avoid verbose warning:

build/minimum-dependency-versions-venv/lib/python3.7/site-packages/sqlalchemy/util/langhelpers.py:637
.../site-packages/sqlalchemy/util/langhelpers.py:637: DeprecationWarning: `formatargspec` is deprecated since Python 3.5. Use `signature` and the `Signature` object directly
d_args = inspect.formatargspec(spec[0][1:])