Document `Resource.duplicate(true)` behavior change in Upgrading to Godot 4.5

This also adds a missing comma in various upgrade guides.

tutorials/migrating/upgrading_to_godot_4.1.rst

@@ -195,7 +195,7 @@ Method ``create_action`` adds a new ``backward_undo_ops`` optional parameter
 Behavior changes
 ----------------
 
-In 4.1 some behavior changes have been introduced, which might require you to adjust your project.
+In 4.1, some behavior changes have been introduced, which might require you to adjust your project.
 
 ==================================================================================================================================================================================================  ===========
 Change                                                                                                                                                                                              Introduced

tutorials/migrating/upgrading_to_godot_4.3.rst

@@ -224,7 +224,7 @@ Type renamed to ``EditorSceneFormatImporterFBX2GLTF``
 Behavior changes
 ----------------
 
-In 4.3 some behavior changes have been introduced, which might require you to adjust your project.
+In 4.3, some behavior changes have been introduced, which might require you to adjust your project.
 
 Core
 ~~~~
@@ -299,7 +299,7 @@ Multiplayer
 
     This is a breaking change for the high-level multiplayer protocol making it incompatible with previous Godot versions.
     Upgrade both your server and client versions to Godot 4.3 to handle this change gracefully.
-    
+
     Note that high-level multiplayer facilities are only ever meant to be compatible with server and client using the same Godot version. It is recommended to implement some kind of version checking.
 
 Rendering

tutorials/migrating/upgrading_to_godot_4.5.rst

@@ -188,7 +188,7 @@ Method ``_get_option_icon`` changes return type from ``ImageTexture`` to ``Textu
 Behavior changes
 ----------------
 
-In 4.5 some behavior changes have been introduced, which might require you to adjust your project.
+In 4.5, some behavior changes have been introduced, which might require you to adjust your project.
 
 3D Model Import
 ~~~~~~~~~~~~~~~
@@ -204,6 +204,16 @@ new behavior, you must change the "Naming Version" option at the bottom of the I
 Core
 ~~~~
 
+.. note::
+
+    :ref:`Resource.duplicate(true) <class_Resource_method_duplicate>` (which performs
+    deep duplication) now only duplicates resources internal to the resource file
+    it's called on. In 4.4, this duplicated everything instead, including external resources.
+    If you were deep-duplicating a resource that contained references to other
+    external resources, those external resources aren't duplicated anymore. You must call
+    :ref:`Resource.duplicate_deep(RESOURCE_DEEP_DUPLICATE_ALL) <class_Resource_method_duplicate_deep>`
+    instead to keep the old behavior.
+
 .. note::
 
     :ref:`ProjectSettings.add_property_info() <class_ProjectSettings_method_add_property_info>`