Actions & Attachments don't work in the `failed` boundary snippet

[PatrickG]

Describe the bug

Since Svelte 5.36.0 actions & attachments don't work inside the failed snippet of a <svelte:boundary> anymore.
Experimental async does not need to be enabled.
Might be related to #16627.

Reproduction

1. Click the "whatever you do, don't click this button" button
2. "ACTION" & "ATTACHMENT" should be logged to the console

• Working in svelte 5.35.7
• Not working in svelte 5.36.0

Logs

System Info

Svelte 5.36.0

Severity

blocking an upgrade