Test showing mismatches after suspending force fallbacks to be shown

[rickhanlonii]

While investigating #28285 I found a possible bug in handling Suspense and mismatches. As the tests show, if the first sibling in a boundary suspends, and the second has a mismatch, we will NOT show a fallback. If the first sibling is a mismatch, and the second sibling suspends, we WILL show a fallback.

Here's a stackbliz showing the behavior on Canary.

This breakage was introduced by: #26380. Before this PR, we would not show a fallback in either case. That PR makes it so that we don't pre-render siblings of suspended trees, so presumably, whatever detection we had to avoid fallbacks on mismatches, requires knowing there's a mismatch in the tree when we suspend.

[react-sizebot]

Comparing: 374fd68...8e3f8ea

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	176.82 kB	176.82 kB	=	55.12 kB	55.12 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	178.81 kB	178.81 kB	=	55.70 kB	55.69 kB
facebook-www/ReactDOM-prod.classic.js	=	593.39 kB	593.39 kB	=	104.69 kB	104.69 kB
facebook-www/ReactDOM-prod.modern.js	=	577.17 kB	577.17 kB	=	101.78 kB	101.78 kB
test_utils/ReactAllWarnings.js	Deleted	67.02 kB	0.00 kB	Deleted	16.42 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	67.02 kB	0.00 kB	Deleted	16.42 kB	0.00 kB

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