Fix an error in decoding tests. #2516

Job	Run time
Test on ubuntu-latest	12m 53s
Bitrot check	4m 17s
Build target wasm32-wasi	3m 58s
Latest build on ubuntu-latest	1m 49s
Test on ubuntu-latest with --features orchard	13m 9s
Latest build on windows-latest	4m 55s
Test on ubuntu-latest with --features unstable-nu6	13m 7s
Latest build on macOS-latest	2m 26s
Clippy (MSRV)	4m 26s
Test on ubuntu-latest with --features zfuture	13m 1s
Clippy (beta)	16s
Test on windows-latest	17m 52s
Code coverage	20m 29s
Test on windows-latest with --features orchard	17m 59s
Intra-doc links	5m 25s
Test on windows-latest with --features unstable-nu6	17m 46s
Rustfmt	12s
Test on windows-latest with --features zfuture	17m 20s
protobuf consistency	4m 14s
UUID validity	3s
Test on macOS-latest	17m 51s
Test on macOS-latest with --features orchard	18m 13s
	3h 31m 41s

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