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Fix warnings about `cfg(fuzzing)` #1697

Job	Run time
Miri tests	42s
Test (ubuntu-latest)	14s
Check Formatting	11s
Test (macos-latest)	22s
Test stable without features (ubuntu-latest)	27s
Test (windows-latest)	1m 54s
Test stable without features (macos-latest)	20s
Test unstable features (ubuntu-latest)	14s
Test stable without features (windows-latest)	1m 13s
Test unstable features (macos-latest)	19s
Test unstable features (windows-latest)	1m 1s
	6m 57s

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