Stop using pygtkcompat

This is basically #8489 (closed) so feel free to reopen that issue instead if you like.

pygobject announced today that pygobject 3.54 will no longer include pygtkcompat. I expect pygobject 3.54 to be released along with GNOME 49 in September.

Therefore please stop using pygtkcompat.

pygtkcompat is used in tryton/gui/window/view_form/view/list.py

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I'd like to point out that pygobject 3.52 has already removed pygtkcompat and this one has been released earlier this month.

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