Dev mode {#each} check breaks with strings

[Conduitry]

Describe the bug
The dev mode validation check for {#each} blocks breaks with strings.

Logs
cannot use 'in' operator to search for "length" in "foo"

To Reproduce
https://svelte.dev/repl/svg-transitions?version=3.19.0

Expected behavior
Same as https://svelte.dev/repl/svg-transitions?version=3.18.2

Stacktraces

Information about your Svelte project:

• Browser independent
• Reproducible in REPL

Severity
Moderate, probably.

Additional context
The check introduced in #4419 apparently throws with strings. We probably want to consider strings to be array-like objects, and so we need to be more permissive with the validation check.

[Conduitry]

The example works again in 3.19.1 - https://svelte.dev/repl/svg-transitions?version=3.19.1 - and will be fixed on https://svelte.dev/examples#svg-transitions as well once unpkg's latest tag caching expires.