Auto merge of #115859 - compiler-errors:effect-fallback, r=fee1-dead

Fallback effects even if types also fallback

`||` is short circuiting, so if we do ty/int var fallback, we *don't* do effect fallback 😸

r? `@fee1-dead` or `@oli-obk`

Fixes #115791
Fixes #115842

Author: bors