bug#52652: FreeCAD requires write access to store for parsetab.py

[Jacob Hrbek]

The FreeCAD on guix with patch 52608 to satisfy the dependency for 
python-ply requires write access to the store to work with OpenSCAD files:

Steps to reproduce:
0. Get FreeCAD and open a new project
2. Navigate to OpenSCAD workbench
3. In top-menu: OpenSCAD -> Add OpenSCAD Element...
4. Try to create `cube()` as **NON**-mesh and expect the following:

ImportCSG Version 0.6a
Start Lex
End Lex
Load Parser
WARNING: Token 'DOT' defined, but not used
WARNING: Token 'WORD' defined, but not used
WARNING: There are 2 unused tokens
WARNING: Couldn't create 'parsetab'. [Errno 30] Read-only file system: 
'/gnu/store/wga178lb0hiwyplv00mpvv6q3i74nqbr-freecad-0.19.2/Mod/OpenSCAD/parsetab.py'
Parser Loaded
Start Parser
size vector
('size', ['1', '1', '1'])
('center', 'false')
cube :  {'size': ['1', '1', '1'], 'center': 'false'}
End Cube
End Parser
[<Part::PartFeature>]
End processing CSG file

--
-- Jacob Hrbek

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