ci: bump actions/cache from 5 to 6 (#79)

Author: dependabot[bot]

.github/workflows/test.yml

@@ -114,7 +114,7 @@ jobs:
           target: ${{ matrix.target }}
           toolchain: ${{ matrix.toolchain }}
       - name: Cache cargo plugins
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ~/.cargo/bin/
           key: ${{ runner.os }}-cargo-plugins