Fix referenced output key in save action readme (#1061)

Co-authored-by: Vipul <vsvipul@github.com>
Co-authored-by: Sankalp Kotewar <98868223+kotewar@users.noreply.github.com>

save/README.md

@@ -54,7 +54,7 @@ Case 1: Where an user would want to reuse the key as it is
 ```yaml
 uses: actions/cache/save@v3
 with:
-    key: ${{ steps.restore-cache.outputs.key }}
+    key: ${{ steps.restore-cache.outputs.cache-primary-key }}
 ```
 
 Case 2: Where the user would want to re-evaluate the key