Turn on useModernStrictMode in test renderers (facebook#31769)

It's on everywhere else, let's turn this on so we can remove it. 

Probably should have been turned on in the test renderer for 19.

Author: rickhanlonii

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -53,7 +53,7 @@ export const enableLegacyHidden = false;
 
 export const enableTransitionTracing = false;
 
-export const useModernStrictMode = false;
+export const useModernStrictMode = true;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
 export const enableFizzExternalRuntime = true;
 export const enableDeferRootSchedulingToMicrotask = true;

packages/shared/forks/ReactFeatureFlags.test-renderer.www.js

@@ -55,7 +55,7 @@ export const enableLegacyHidden = false;
 
 export const enableTransitionTracing = false;
 
-export const useModernStrictMode = false;
+export const useModernStrictMode = true;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
 export const enableFizzExternalRuntime = false;
 export const enableDeferRootSchedulingToMicrotask = true;