fix: only inject push/pop/$$props in SSR components when necessary

[Rich-Harris]

import * as $ from "svelte/internal/server";

-export default function App($$payload, $$props) {
+export default function App($$payload) {
- $.push();
  $$payload.out += `<h1>hello world</h1>`;
- $.pop();
}

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The changes in this PR will be included in the next version bump.

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