use PySequence in BlsCache::update()

[arvidn]

in chia-blockchain we pass in a list of (bytes32, GTElement), and even though bytes32 is a bytes, the fact that the update() function takes a List means it's not covariant.

This is meant to fix that.

[coveralls-official]

Pull Request Test Coverage Report for Build 10997493863

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 83.303%

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Totals
Change from base Build 10997285527:	0.0%
Covered Lines:	12378
Relevant Lines:	14859

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💛 - Coveralls