fixes#8860
This contains a small but unfortunately unavoidable breaking change: If you used `never` to type that the second parameter of `createEventDispatcher` shouldn't be set or that the action accepts no parameters (which the docs recommended for a short time), then you need to change that to `null` and `undefined` respectively
dispatch('noArgument', 'surprise'); // error, cannot pass an argument
dispatch('noArgument', 'surprise'); // error, cannot pass an argument
```
```
- `Action` and `ActionReturn` have a default parameter type of `never` now, which means you need to type the generic if you want to specify that this action receives a parameter. The migration script will migrate this automatically ([#7442](https://github.com/sveltejs/svelte/pull/7442))
- `Action` and `ActionReturn` have a default parameter type of `undefined` now, which means you need to type the generic if you want to specify that this action receives a parameter. The migration script will migrate this automatically ([#7442](https://github.com/sveltejs/svelte/pull/7442))
```diff
```diff
-const action: Action = (node, params) => { .. } // this is now an error, as params is expected to not exist
-const action: Action = (node, params) => { .. } // this is now an error if you use params in any way
+const action: Action<HTMLElement,string> = (node, params) => { .. } // params is of type string
+const action: Action<HTMLElement,string> = (node, params) => { .. } // params is of type string