Release zcash_proofs version 0.20.0 #6070

Job	Run time
Check ZFuture build on Linux	27s
Test on Linux	6m 37s
Check ZFuture build on macOS	35s
Bitrot check	1m 32s
Test Orchard on Linux	8m 45s
Latest build on ubuntu-latest	2m 3s
Check ZFuture build on Windows	2m 45s
Test NU7 on Linux	6m 30s
Latest build on windows-latest	5m 50s
Test on macOS	8m 24s
Latest build on macOS-latest	1m 53s
Test Orchard on macOS	10m 44s
Build target wasm32-wasi	57s
Clippy (MSRV)	1m 17s
Test on Windows	13m 18s
Test Orchard on Windows	15m 16s
Clippy (beta)	15s
Test NU7 on Windows	11m 3s
Code coverage	1h 42m 12s
Intra-doc links	2m 8s
Rustfmt	16s
protobuf consistency	1m 1s
UUID validity	3s
Required status checks have passed	1s
	3h 23m 52s

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