Update filename of Misc/stable_abi.toml (GH-847)

CPython change: python/cpython#92026
Heads-up/discussion: https://mail.python.org/archives/list/[email protected]/thread/C66LFKFO23BACJ673FVF7E2VS5TBP6DW/

I didn't add a note for older versions: released versions
should *never* get new stable ABI entries.

Author: encukou

c-api.rst

@@ -212,17 +212,17 @@ Adding a new definition to the Limited API
 
   with the ``yy`` corresponding to the target CPython version, e.g.
   ``0x030A0000`` for Python 3.10.
-- Append an entry to the Stable ABI manifest, ``Misc/stable_abi.txt``.
+- Append an entry to the Stable ABI manifest, ``Misc/stable_abi.toml``
 - Regenerate the autogenerated files using ``make regen-limited-abi``.
   On platforms without ``make``, run this command directly:
 
   .. code-block:: shell
 
-     ./python ./Tools/scripts/stable_abi.py --generate-all ./Misc/stable_abi.txt
+     ./python ./Tools/scripts/stable_abi.py --generate-all ./Misc/stable_abi.toml
 
 - Build Python and check the using ``make check-limited-abi``.
   On platforms without ``make``, run this command directly:
 
   .. code-block:: shell
 
-    ./python ./Tools/scripts/stable_abi.py --all ./Misc/stable_abi.txt
+    ./python ./Tools/scripts/stable_abi.py --all ./Misc/stable_abi.toml