extend softfork test to cover the hard fork flag #1767

Job	Run time
Wheel on macos-latest py-3.8	2m 41s
Wheel on ubuntu-latest py-3.8	2m 41s
Checks	49s
Wheel on windows-latest py-3.8	2m 23s
Run fuzz targets (macos-latest, 3.8)	13m 27s
coverage	7m 55s
Run fuzz targets (ubuntu-latest, 3.8)	15m 35s
Unit tests (macos-latest, 3.8)	3m 12s
Unit tests (ubuntu-latest, 3.8)	3m 28s
Unit tests (windows-latest, 3.8)	6m 5s
Upload to PyPI	23s
	58m 39s

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