Update examples.md

Update the example for rust so that the cache key actually works as intended

examples.md

@@ -456,7 +456,9 @@ When dependencies are installed later in the workflow, we must specify the same
       ~/.cargo/registry
       ~/.cargo/git
       target
-    key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+    key: cargo-${{ hashFiles('**/Cargo.lock') }}
+    restore-keys: |
+      cargo-
 ```
 
 ## Scala - SBT