Follow no-unsafe-function-type lint rule (#14696)

This rule comes from `typescript-eslint`:
https://typescript-eslint.io/rules/no-unsafe-function-type/

We don't have it enabled yet, but in v8 it's part of the "recommended"
preset:
https://typescript-eslint.io/blog/announcing-typescript-eslint-v8/#updated-configuration-rules

In order to keep the upgrade to that version as small as possible, this
change pre-emptively fixes code considered incorrect by that rule. The
only instance occurs in `EpicButton`, and would previously have been
caught by the `ban-types` rule, if that were not disabled for this line.
`ban-types` has been removed and replaced by `no-unsafe-function-type`
for this particular issue, hence why the error has reappeared:
https://typescript-eslint.io/blog/announcing-typescript-eslint-v8/#replacement-of-ban-types

We could update the `eslint-disable-next-line` comment, but there is a
more specific type that can be used in this case, as mentioned in the
documentation for the rule:

```ts
() => void;
```

Author: JamieB-gu

dotcom-rendering/src/components/marketing/epics/ctas/EpicButton.tsx

@@ -43,8 +43,7 @@ type Props = {
 	// A function will render a <Button>
 	// A string will render a <LinkButton>
 	// Both using the same interface
-	// eslint-disable-next-line @typescript-eslint/ban-types
-	onClickAction: Function | Url;
+	onClickAction: (() => void) | Url;
 	submitComponentEvent?: (event: ComponentEvent) => void;
 	children: React.ReactElement | string;
 	priority?: 'primary' | 'secondary';