Change `opt-level` from 3 to 2 for the test profile #6029

Job	Run time
Build target wasm32-wasi	52s
Latest build on ubuntu-latest	2m 6s
Latest build on windows-latest	5m 8s
Bitrot check	1m 30s
Latest build on macOS-latest	1m 35s
Clippy (MSRV)	1m 17s
Clippy (beta)	11s
Code coverage	56m 36s
Intra-doc links	2m 13s
Rustfmt	12s
protobuf consistency	1m 4s
UUID validity	2s
Check ZFuture build on Linux	30s
Check ZFuture build on macOS	32s
Test on Linux	5m 53s
Test Orchard on Linux	7m 23s
Check ZFuture build on Windows	1m 40s
Test NU7 on Linux	5m 53s
Test on macOS	10m 38s
Test Orchard on macOS	9m 31s
Test on Windows	11m 59s
Test Orchard on Windows	15m 22s
Test NU7 on Windows	12m 13s
Required status checks have passed	1s
	2h 34m 21s

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