Fix bug where we calculated the relative path of recurisive copies wrong

Fixes #11470

lib/ansible/plugins/action/copy.py

@@ -90,7 +90,7 @@ class ActionModule(ActionBase):
         if os.path.isdir(source):
             # Get the amount of spaces to remove to get the relative path.
             if source_trailing_slash:
-                sz = len(source)
+                sz = len(source) + 1
             else:
                 sz = len(source.rsplit('/', 1)[0]) + 1