[eslint-plugin] Stop warning for head element in app/layout on Windows (#42336)
## Bug

When trying to use app directory on Windows, the automatically created
`Layout.tsx` get's a lint problem for having a `<head>` element.
## Solution
Update the rule to check paths using `path.sep` rather than hardcoded
`/`
I also checked with `path.posix.sep` because some other rules was doing
that (both `path.sep` and `path.posix.sep`), so I'm just following
pattern