Fix documents broken by multi-line f-string formulas on Python 3.12+ (#2518)

Such a formula generated code that did not compile, failing
gencode.make_module() for the whole schema. The document became
unusable, reporting KeyError '<table>' or "'DocModel' object has no
attribute 'tables'" for every action.

Affects engines on 3.12+: since 1.7.13 that means the pyodide sandbox
(Pyodide 0.28 bundles CPython 3.13), and source installs with a recent
python3. Reported in

https://community.getgrist.com/t/document-broken-when-updating-to-1-7-16-or-higher/14105

Also on 3.13: friendly-traceback needs an `executing` upgrade. Added a
CI leg on 3.13.