Parse argument of `pijul log --output-format` strictly

Created by  7qFsmcJTAmyi5DxiNk265yTyKeTGNeoqjQfzksWAeGkH  on November 7, 2022
7P7G4J5ZT4S5BP6VAN226Z7CRZXEEVO5YHJ6IFMW27NHBR5TDJRAC
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