Log Message:
finance/ledger, finance/ledger32: Mark incompatible with Python 3.12.

These still use PyUnicode_GET_SIZE, which was removed in Python 3.12:

https://peps.python.org/pep-0623/

Set Python_EXECUTABLE explicitly so they don't inadvertently pick up
bin/python3.12.

No revbump because finance/ledger and finance/ledger32 currently
don't build at all with pkgsrcwide default of Python 3.12.

The issue has been fixed upstream so it can probably be removed in
the next finance/ledger update:

https://github.com/ledger/ledger/issues/2332

And with any luck, finance/ledger32 can be removed eventually, now
that upstream has acknowledged the bug that motivated it:

https://github.com/ledger/ledger/issues/2355
(dup of https://github.com/ledger/ledger/issues/2318)