ffa22212560c9e7a8692cb8982d9b3b507ee9af1 tests: Pass fuzzing inputs as constant references (practicalswift)
Pull request description:
Pass fuzzing inputs as constant references.
Split out from #17009 as suggested by MarcoFalke in https://github.com/bitcoin/bitcoin/pull/17009#discussion_r331502028.
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Backport of Core PR17069