Update actions/cache action to v6 (#35)

Author: renovate[bot]

.github/actions/cache_cargo/action.yml

@@ -4,7 +4,7 @@ runs:
   using: composite
   steps:
     - name: Cache cargo registry
-      uses: actions/cache@v5
+      uses: actions/cache@v6
       with:
         path: |
           ~/.cargo/registry