Don't set a propagate type if the variable has already the same static type.

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

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index 9b9e88dd0c39bf2c46374fc9a53053ac91086483..475c5b09df4550e1dedfc45f3b02fbcf5b5f5a07 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -10437,6 +10437,10 @@ class ResolverVisitor extends ScopedVisitor {
     }
     DartType currentType = _overrideManager.getBestType(element);
 
+    if (potentialType == currentType) {
+      return;
+    }
+
     // If we aren't allowing precision loss then the third and fourth conditions
     // check that we aren't losing precision.
     //