Allow use of `setContext` in async contexts

[sirkostya009]

Describe the problem

no pun intended.

ex.:

<script>
	import { setContext } from "svelte";

	async function foo() {
		return await 1;
	}

	setContext({}, await foo())
</script>

causes errors like:

Svelte error: missing_context
Context was not set in a parent component
https://svelte.dev/e/missing_context

Describe the proposed solution

Make it work

Importance

would make my life easier

[dummdidumm]

this is on purpose so that we can later have the possibility to optimize the script tag to be non-blocking. If we decide we don't want to do that we can lift this context restriction