Keyed each block is updated unnecessarily

[Rich-Harris]

Describe the bug
In this app, via this SO question, a keyed each block is updated when any variable is reassigned, rather than only when the dependencies of the block are.

The update_keyed_each(...) call isn't being wrapped in an if (dirty & ...) block, as it should.

To Reproduce
https://svelte.dev/repl/191e46b4229043a89ac5018658a84ecb?version=3.18.1

Expected behavior
Adding items via the input shouldn't have any effect, because the array is being mutated but not reassigned.

Severity
Low

[Conduitry]

This is no longer happening in 3.19.0.