fix code snippet in Fit generic regressor

Issue #1296 resolved
Andreas Rabe created an issue

Kann Algorithmus nicht ausführen
Traceback (most recent call last):
File
"C:\Users/PC/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\enmapboxplugin\enmapboxprocessing\algo
rithm\fitregressoralgorithmbase.py", line 67, in checkParameterValues
self.parameterAsRegressor(parameters, self.P_REGRESSOR, context)
File "C:\Users/PC/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\enmapboxplugin\sitepackages\
typeguard\__init__.py", line 903, in wrapper
retval = func(*args, **kwargs)
File
"C:\Users/PC/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\enmapboxplugin\enmapboxprocessing\algo
rithm\fitregressoralgorithmbase.py", line 59, in parameterAsRegressor
return namespace['regressor']