Add missing feature flag conditional #4852

Job	Run time
Latest build on ubuntu-latest	2m 4s
Latest build on windows-latest	3m 53s
Latest build on macOS-latest	4m 47s
Clippy (MSRV)	5m 7s
Build target wasm32-wasi	4m 32s
Bitrot check	4m 42s
Clippy (beta)	12s
Test on ubuntu-latest	13m 58s
Code coverage	21m 40s
Test on ubuntu-latest with --features orchard	14m 17s
Test on ubuntu-latest with --features unstable-nu6	13m 43s
Intra-doc links	5m 17s
Rustfmt	11s
Test on ubuntu-latest with --features zfuture	14m 44s
Test on windows-latest	18m 13s
protobuf consistency	4m 25s
Test on windows-latest with --features orchard	18m 28s
UUID validity	6s
Test on windows-latest with --features unstable-nu6	18m 2s
Test on windows-latest with --features zfuture	18m 2s
Test on macOS-latest	16m 8s
Test on macOS-latest with --features orchard	21m 27s
	3h 43m 58s

Provide feedback