add generated test cases for the sha256 operator #1705

Job	Run time
Wheel on macos-latest py-3.7	3m 57s
Wheel on ubuntu-latest py-3.7	2m 14s
Wheel on windows-latest py-3.7	3m 33s
Checks	48s
Run fuzz targets (macos-latest, 3.7)	32m 27s
Run fuzz targets (ubuntu-latest, 3.7)	15m 23s
coverage	9m 43s
Unit tests (macos-latest, 3.7)	9m 39s
Unit tests (ubuntu-latest, 3.7)	3m 25s
Unit tests (windows-latest, 3.7)	6m 16s
Upload to PyPI	24s
	1h 27m 49s

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