[BUGFIX] Fix getter/setter tests for model property types 'file' and 'image'

The property types 'file' and 'image' use FileReference from
Extbase FAL implementation.
The generated unit test for the getter/setter of these model
properties test for FileReference.

Change-Id: I71ef71ea0efca8707e5c724a7a18dc3f04c2343d
Resolves: #58111
Releases: 6.2
Reviewed-on: https://review.typo3.org/29697
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen