add whatsnew entry for PyUnstable_SetImmortal and PyDatetime_IMPORT (#144830)

Author: kumaraditya303

Doc/c-api/datetime.rst

@@ -30,6 +30,10 @@ macros.
 
       This is not compatible with subinterpreters.
 
+   .. versionchanged:: 3.15
+
+      This macro is now thread safe.
+
 .. c:type:: PyDateTime_CAPI
 
    Structure containing the fields for the datetime C API.
@@ -44,6 +48,11 @@ macros.
 
    This variable is only available once :c:macro:`PyDateTime_IMPORT` succeeds.
 
+   .. versionchanged:: 3.15
+
+      This variable should not be accessed directly as direct access is not thread-safe.
+      Use :c:func:`PyDateTime_IMPORT` instead.
+
 .. c:type:: PyDateTime_Date
 
    This subtype of :c:type:`PyObject` represents a Python date object.

Doc/whatsnew/3.15.rst

@@ -1563,6 +1563,8 @@ New features
   thread state.
   (Contributed by Victor Stinner in :gh:`139653`.)
 
+* Add :c:func:`PyUnstable_SetImmortal` C-API function to mark objects as :term:`immortal`.
+  (Contributed by Kumar Aditya in :gh:`143300`.)
 
 Changed C APIs
 --------------
@@ -1571,6 +1573,9 @@ Changed C APIs
   flag is set then :c:macro:`Py_TPFLAGS_HAVE_GC` must be set too.
   (Contributed by Sergey Miryanov in :gh:`134786`.)
 
+* :c:macro:`PyDateTime_IMPORT` is now thread safe. Code that directly checks ``PyDateTimeAPI``
+  for ``NULL`` should be updated to call :c:macro:`PyDateTime_IMPORT` instead.
+  (Contributed by Kumar Aditya in :gh:`141563`.)
 
 Porting to Python 3.15
 ----------------------