Rewrite test suite to accommodate compatibility across python 3.8/3.9 boundary

[ctk3b]

See python 3.9 failures here: https://github.com/ctk3b/borderline/runs/3627419435

[ctk3b]

Documented problem here:

borderline/borderline.py

Lines 36 to 43 in 601c5b3

	Notes
	-----
	`ast.dump` does not produce identical results across python versions. If you
	are relying on grandfather files, you may need to regenerate them when updating
	python versions.
	Specifically, from python 3.8->3.9, `Import` and `ImportFrom` nodes no longer
	`ast.dump` an `asname` attribute.

[ctk3b]

3.9 works just fine but we'd have to rewrite the unit tests to accommodate differences across python versions