chore: Allow Portal's hidden SSR placeholder in the SSR test

[TrevorBurnham]

This PR updates a test assertion that will fail once cloudscape-design/component-toolkit#249 is merged. It should be merged first to prevent the tests in this repo from failing.

Description

Portal renders a hidden probe span on its first render so its layout effect can read ref.current.ownerDocument. That span was gated on typeof document !== 'undefined', so the server emitted nothing while the client's first render emitted the span — a server/client branch on a DOM global, which React reports as Hydration failed because the server rendered HTML didn't match the client before discarding and re-rendering the subtree. The toolkit fix renders the span during SSR too, so both passes agree.

Portal is the sole root of both InternalModal (src/modal/internal.tsx:82) and Tooltip (src/internal/components/tooltip/index.tsx:73), so their server markup is the Portal's output. That takes it from "" to <span style="display:none"></span>, and this assertion fails:

if (componentName === 'modal' || componentName === 'tooltip') {
  // modal and tooltip use portal API which does not work on server and returns an empty content
  expect(content.length).toEqual(0);
}

The comment also encodes the assumption the toolkit fix invalidates — the portal API not working on the server is exactly why the first render has to match, not a reason to emit nothing.

The new assertion in this PR asserts what the test actually cares about: the portaled content is not in the server markup, and whatever is emitted is either nothing or the hidden placeholder.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.66%. Comparing base (701afeb) to head (36c9613).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4908   +/-   ##
=======================================
  Coverage   97.66%   97.66%           
=======================================
  Files         958      958           
  Lines       31317    31317           
  Branches    11566    11565    -1     
=======================================
  Hits        30585    30585           
- Misses        686      725   +39     
+ Partials       46        7   -39     

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[TrevorBurnham]

CI run failures appear to be due to an issue on main, unrelated to the changes in this PR.