fix #27408, reverts "ignore dynamic in inference"

pkg/analyzer/lib/src/generated/type_system.dart

Index: pkg/analyzer/lib/src/generated/type_system.dart
diff --git a/pkg/analyzer/lib/src/generated/type_system.dart b/pkg/analyzer/lib/src/generated/type_system.dart
index 4899d9a2821173456277694060e6a695df1bc2b5..0488553c43014ca14e9210c463bb5279263b57a8 100644
--- a/pkg/analyzer/lib/src/generated/type_system.dart
+++ b/pkg/analyzer/lib/src/generated/type_system.dart
@@ -1640,12 +1640,8 @@ class _StrongInferenceTypeSystem extends StrongTypeSystemImpl {
         // We already know L <: T2, for some L.
         // So update L to reflect the new constraint LUB(L, T1) <: T2
         //
-
-        // Heuristic: we intentionally ignore `dynamic` when doing inference.
-        if (!t1.isDynamic) {
-          bound.lower =
-              _typeSystem.getLeastUpperBound(_typeProvider, bound.lower, t1);
-        }
+        bound.lower =
+            _typeSystem.getLeastUpperBound(_typeProvider, bound.lower, t1);
         // Optimistically assume we will be able to satisfy the constraint.
         return true;
       }