Allow use of caches 'read-only'

To avoid evicting useful entries, some pipeline may benefit from using existing
cache entries without writing any changes back to the cache.

Fixes #62

action.yml

@@ -51,6 +51,10 @@ inputs:
     description: Whether to restore only if exact match, default to 'false'
     required: false
     default: false
+  cache-read-only:
+    description: When 'true', existing entries will be read from the cache but no entries will be written
+    required: false
+    default: false
 
 outputs:
   build-scan-url: