cext: fix Python 3.11 compatibility - Py_SIZE is not an lvalue (issue6610)
Py_SIZE was made a static inline function during Python 3.10 development, as
described on https://vstinner.github.io/c-api-opaque-structures.html .
e92ca942ddca updated the Mercurial code base accordingly, but somehow missed a
couple of cases introduced long time ago in a8c948ee3668.
The Python change was dropped for 3.10, but is coming back again in 3.11 .
$ cat >> $HGRCPATH << EOF
> [extensions]
> fastannotate=
> EOF
$ hg init repo
$ cd repo
changes to whitespaces
$ cat >> a << EOF
> 1
>
>
> 2
> EOF
$ hg commit -qAm '1'
$ cat > a << EOF
> 1
>
> 2
>
>
> 3
> EOF
$ hg commit -m 2
$ hg fastannotate -wB a
0: 1
0:
1: 2
0:
1:
1: 3