Relax the action input check for actions that require no input (#6357)
When the tool requires no input, the LLM often gives something like
this:
```json
{
"action": "just_do_it"
}
```
I have attempted to enhance the prompt, but it doesn't appear to be
functioning effectively. Therefore, I believe we should consider easing
the check a little bit.
Signed-off-by: Xiaochao Dong (@damnever) <the.xcdong@gmail.com>