fix: Correct typo in adk run --resume help

Fix by--save_session

```
  --resume FILE      The json file that contains a previously saved session
                     (by--save_session option). The previous session will be
                     re-displayed. And user can continue to interact with the
                     agent.
```

Author: ftnext

src/google/adk/cli/cli_tools_click.py

@@ -237,7 +237,7 @@ def validate_exclusive(ctx, param, value):
     ),
     help=(
         "The json file that contains a previously saved session (by"
-        "--save_session option). The previous session will be re-displayed. And"
+        " --save_session option). The previous session will be re-displayed. And"
         " user can continue to interact with the agent."
     ),
     callback=validate_exclusive,