[3.15] Correct Stable ABI documentation for METH_FASTCALL (GH-149593) (GH-150853)

The current documentation says:

>
> METH_FASTCALL
>    Part of the Stable ABI since version 3.7.
>
> [...]
>
>   Added in version 3.7.
>
>    Changed in version 3.10: METH_FASTCALL is now part of the stable ABI.

so is contradictory about when it was added to the Stable ABI.  Looking at the header it seems like 3.10 is right.
(cherry picked from commit 58beae7)

Co-authored-by: da-woods <dw-git@d-woods.co.uk>

Author: miss-islington

Doc/data/stable_abi.dat

@@ -1813,7 +1813,6 @@
 [const.METH_COEXIST]
     added = '3.2'
 # METH_STACKLESS is undocumented
-# METH_FASTCALL is not part of limited API.
 
 # The following are defined in private headers, but historically
 # they were exported as part of the stable ABI.
@@ -2149,8 +2148,6 @@
 
 # New method flags in 3.7 (PEP 590):
 
-[const.METH_FASTCALL]
-    added = '3.7'
 [const.METH_METHOD]
     added = '3.7'
 
@@ -2300,6 +2297,10 @@
 [data.PyStructSequence_UnnamedField]
     added = '3.11'
 
+# Added in 3.7 but in the Stable ABI from 3.10
+[const.METH_FASTCALL]
+    added = '3.10'
+
 # Add stable Py_buffer API in Python 3.11 (https://bugs.python.org/issue45459)
 [struct.Py_buffer]
     added = '3.11'