In GitHub and in these tests the slots_component takes keyword
arguments, not `args`. The `args` variable needs to be double splatted
in the initalization caller.

The warnings can be seen when running the tests before this change was
introduced.

Fixes:

```
view_component/lib/view_component/slotable.rb:98: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
view_component/test/app/components/slots_component.rb:18: warning: The called method `initialize' is defined here
```