Release zcash_client_backend version 0.15.0 #6066

Job	Run time
Latest build on ubuntu-latest	2m 6s
Latest build on windows-latest	3m 53s
Latest build on macOS-latest	2m 13s
Check ZFuture build on Linux	1m 57s
Check ZFuture build on macOS	34s
Check ZFuture build on Windows	4m 56s
Bitrot check	1m 31s
Build target wasm32-wasi	52s
Clippy (MSRV)	1m 19s
Clippy (beta)	11s
Test on Linux	4m 29s
Test Orchard on Linux	4m 44s
Test NU7 on Linux	4m 34s
Code coverage	1h 33m 26s
Intra-doc links	2m 12s
Test on macOS	1s
Test Orchard on macOS	1s
Rustfmt	15s
Test on Windows	4m 33s
protobuf consistency	1m 6s
Test Orchard on Windows	4m 33s
Test NU7 on Windows	4m 34s
UUID validity	6s
Required status checks have passed	1s
	2h 24m 7s

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