CHIA-2220 Fix a typo when picking the best unfinished block in test_request_unfinished_block2

[AmineKhaldi]

At this point, we already know that unf.foliage.foliage_transaction_block_hash is not None, but in order to compare it with our current best unfinished block, best_unf.foliage.foliage_transaction_block_hash must not be None as well.

[coveralls-official]

Pull Request Test Coverage Report for Build 12906301067

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 29 unchanged lines in 8 files lost coverage.
• Overall coverage increased (+0.001%) to 91.515%

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Files with Coverage Reduction	New Missed Lines	%
chia/_tests/simulation/test_simulation.py	1	96.45%
chia/wallet/util/wallet_sync_utils.py	1	86.14%
chia/full_node/full_node_api.py	1	84.38%
chia/timelord/timelord_launcher.py	1	91.43%
chia/full_node/full_node.py	1	86.63%
chia/server/node_discovery.py	2	81.68%
chia/wallet/wallet_node.py	8	87.82%
chia/timelord/timelord.py	14	78.2%

Totals
Change from base Build 12894248841:	0.001%
Covered Lines:	105318
Relevant Lines:	114908

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💛 - Coveralls