feat: add save-if option, closes #66 (#91)

action.yml

@@ -28,6 +28,10 @@ inputs:
   cache-on-failure:
     description: "Cache even if the build fails. Defaults to false."
     required: false
+  save-if:
+    description: "Determiners whether the cache should be saved. If `false`, the cache is only restored."
+    required: false
+    default: "true"
 outputs:
   cache-hit:
     description: "A boolean value that indicates an exact match was found."