Fix wxGUI Field calculator wx.ListBox widget choices argument

[tmszi]

Reproduce:

1. Add some vector map layer in Layer Manager
2. Open Attribute Table Manager
3. On the Browse data page right click on the some column to invoke menu and click on the Field calculator menu item

Error message appear in the Console page:

Traceback (most recent call last):
  File "/usr/local/grass79/gui/wxpython/dbmgr/base.py", line
621, in OnFieldCalculator

self._col).GetText())
  File
"/usr/local/grass79/gui/wxpython/dbmgr/sqlbuilder.py", line
635, in __init__

modeChoices=modeChoices, layer=layer)
  File
"/usr/local/grass79/gui/wxpython/dbmgr/sqlbuilder.py", line
82, in __init__

self._doLayout(modeChoices)
  File
"/usr/local/grass79/gui/wxpython/dbmgr/sqlbuilder.py", line
708, in _doLayout

style=wx.LB_SORT)
TypeError
:
ListBox(): arguments did not match any overloaded call:
  overload 1: 'parent' is not a valid keyword argument
  overload 2: argument 'choices' has unexpected type
'dict_keys'