Test for ReactTestRenderer

[kassens]

This is a repro for a breakage that #28672 would introduce for legacy sync rendering.

[react-sizebot]

Comparing: a73c345...633df5a

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	=	176.69 kB	176.69 kB	=	54.93 kB	54.93 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	173.09 kB	173.09 kB	=	53.94 kB	53.94 kB
facebook-www/ReactDOM-prod.classic.js	=	592.87 kB	592.87 kB	=	104.00 kB	104.00 kB
facebook-www/ReactDOM-prod.modern.js	=	574.56 kB	574.56 kB	=	101.02 kB	101.02 kB
test_utils/ReactAllWarnings.js	Deleted	65.05 kB	0.00 kB	Deleted	16.26 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	65.05 kB	0.00 kB	Deleted	16.26 kB	0.00 kB

Generated by 🚫 dangerJS against 633df5a

[rickhanlonii]

Kinda sucky that this is test-renderer only, we should migrate those tests