fix reactive updates not reflected when handle promise

[tanhauhau]

Fix #3660

Added a test that would fail otherwise (test/runtime/samples/await-set-simultaneous-reactive/)

When flushing changes after promise, the newly attached block is not updated.
This is more obvious, when the newly attached block props takes value from a reactive declared variables, because their value only changed right before patching the dom

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Tests

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[Conduitry]

It doesn't look like this file is actually used in the test.