ci: isolate clippy cache from stable-toolchain jobs

Clippy uses nightly while other jobs use stable, so sharing
the same rust-cache key causes clippy to restore incompatible
artifacts and recompile from scratch on every run.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kariy

.github/workflows/test.yml

@@ -146,7 +146,7 @@ jobs:
             - uses: Swatinem/rust-cache@v2
               with:
                   key: ci-${{ github.job }}
-                  shared-key: katana-ci-cache
+                  shared-key: katana-ci-cache-nightly
 
             - name: Download test artifacts
               uses: actions/download-artifact@v5