[CI] only show error logs for Mysticeti tests (MystenLabs#16610)

## Description 

Reduce logging noise.

## Test Plan 


https://github.com/MystenLabs/sui/actions/runs/8242605824/job/22541828303

---
If your changes are not user-facing and do not break anything, you can
skip the following section. Otherwise, please briefly describe what has
changed under the Release Notes section.

### Type of Change (Check all that apply)

- [ ] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

.github/workflows/mysticeti.yml

@@ -9,6 +9,9 @@ env:
   # Enable Mysticeti in tests.
   CONSENSUS: "mysticeti"
 
+  # Reduce logging noise.
+  RUST_LOG: "error"
+
   CARGO_TERM_COLOR: always
   # Disable incremental compilation.
   #