tests: fix clippy::redundant_pattern_matching finding #769

Job	Run time
Build wasm32	24s
Format	11s
Clippy	13s
Build + test (stable, ubuntu-latest)	30s
Smoke-test fuzzing targets	1m 8s
Build + test (beta, ubuntu-latest)	29s
msrv (ubuntu-latest)	33s
Build + test (nightly, ubuntu-latest)	27s
Check side-channels on base64 decoder	41s
Check semver compatibility	13s
Build + test (macos-latest, stable)	19s
msrv (macos-latest)	1m 5s
Build + test (windows-latest, stable)	53s
msrv (windows-latest)	49s
	7m 55s

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