Upgrade leak_tracker. (#125272)

Author: polina-c

packages/flutter/pubspec.yaml

@@ -22,7 +22,7 @@ dev_dependencies:
   flutter_goldens:
     sdk: flutter
   fake_async: 1.3.1
-  leak_tracker: 3.0.1
+  leak_tracker: 4.0.0
 
   _fe_analyzer_shared: 58.0.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   analyzer: 5.10.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
@@ -70,4 +70,4 @@ dev_dependencies:
   webkit_inspection_protocol: 1.2.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   yaml: 3.1.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
 
-# PUBSPEC CHECKSUM: 5221
+# PUBSPEC CHECKSUM: 5a21