Add ABI dump to .gitignore

[encukou]

The ABI is only checked in maintenance branches, but it is sometimes useful to generate it for main.

• The resulting file should be ignored in main.
• The file should be created if it doesn't exist.

If this goes in, some “make maintenance branch” RM checklist/script will need a “remove Doc/data/python*.abi from .gitignore” entry.

@pablogsal, this could be combined with #94135

[arhadthedev]

remove Doc/data/python*.abi from .gitignore

Calling git add with --force allows to keep gitignore unmodified:

-f, --force
Allow adding otherwise ignored files.

[encukou]

Yes, but AFAIK there are then warnings when you update a file that's ignored but tracked anyway.
The maintenance branches need some changes anyway – adding the CI check, at least – so I asume it's not a big burden to update .gitignore.

[pablogsal]

@pablogsal, this could be combined with #94135

@encukou do you want me to add this change to that PR?

[encukou]

Go ahead!