[act] Wrap IsThisRendererActing in DEV check

So that it doesn't leak into the production bundle. Follow-up to facebook#16240.

Author: acdlite

packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -1034,7 +1034,11 @@ function renderRoot(
         hasNotProcessedNewUpdates &&
         !isSync &&
         // do not delay if we're inside an act() scope
-        !(flushSuspenseFallbacksInTests && IsThisRendererActing.current)
+        !(
+          __DEV__ &&
+          flushSuspenseFallbacksInTests &&
+          IsThisRendererActing.current
+        )
       ) {
         // If we have not processed any new updates during this pass, then this is
         // either a retry of an existing fallback state or a hidden tree.
@@ -1075,7 +1079,11 @@ function renderRoot(
       if (
         !isSync &&
         // do not delay if we're inside an act() scope
-        !(flushSuspenseFallbacksInTests && IsThisRendererActing.current)
+        !(
+          __DEV__ &&
+          flushSuspenseFallbacksInTests &&
+          IsThisRendererActing.current
+        )
       ) {
         // We're suspended in a state that should be avoided. We'll try to avoid committing
         // it for as long as the timeouts let us.
@@ -1148,7 +1156,11 @@ function renderRoot(
       if (
         !isSync &&
         // do not delay if we're inside an act() scope
-        !(flushSuspenseFallbacksInTests && IsThisRendererActing.current) &&
+        !(
+          __DEV__ &&
+          flushSuspenseFallbacksInTests &&
+          IsThisRendererActing.current
+        ) &&
         workInProgressRootLatestProcessedExpirationTime !== Sync &&
         workInProgressRootCanSuspendUsingConfig !== null
       ) {