bpo-44441: _PyImport_Fini2() resets PyImport_Inittab (GH-26874) (GH-26877)

Py_RunMain() now resets PyImport_Inittab to its initial value at
exit. It must be possible to call PyImport_AppendInittab() or
PyImport_ExtendInittab() at each Python initialization.

(cherry picked from commit 489699ca05bed5cfd10e847d8580840812b476cd)
diff --git a/Doc/c-api/import.rst b/Doc/c-api/import.rst
index c6fc330..d2ae6b6 100644
--- a/Doc/c-api/import.rst
+++ b/Doc/c-api/import.rst
@@ -299,4 +299,8 @@
    field; failure to provide the sentinel value can result in a memory fault.
    Returns ``0`` on success or ``-1`` if insufficient memory could be allocated to
    extend the internal table.  In the event of failure, no modules are added to the
-   internal table.  This should be called before :c:func:`Py_Initialize`.
+   internal table.  This must be called before :c:func:`Py_Initialize`.
+
+   If Python is initialized multiple times, :c:func:`PyImport_AppendInittab` or
+   :c:func:`PyImport_ExtendInittab` must be called before each Python
+   initialization.