qtvcp: fix undefined name in gcode_editor Qsci import fallback

The PyQt5 branch of the QScintilla import fallback caught ImportError
without binding it (no 'as e') but then passed exc_info=e to LOG.critical,
raising NameError. Because sys.excepthook is installed at qtvcp startup and
pops a modal error dialog, that NameError turns a missing python3-pyqt5.qsci
into an indefinite hang (the dialog blocks forever under headless/CI) instead
of a clean exit.

Bind the exception as e and sys.exit(1), matching the PyQt6 branch below.

Author: grandixximo

lib/python/qtvcp/widgets/gcode_editor.py

@@ -62,8 +62,9 @@
     if qtpy.PYQT5:
         try:
             from PyQt5.Qsci import QsciScintilla, QsciLexerCustom, QsciLexerPython
-        except ImportError:
+        except ImportError as e:
             LOG.critical("Can't import QsciScintilla - is package python3-pyqt5.qsci installed?", exc_info=e)
+            sys.exit(1)
     else:
         try:
             from PyQt6.Qsci import QsciScintilla, QsciLexerCustom, QsciLexerPython