misc: allow prefilling file fields with a dictionary (#25385)

tests/form_pages/test_file_field.py

@@ -464,9 +464,9 @@ def test_form_file_field_with_wrong_value(pub):
     assert pub.loggederror_class.count() == 1
     logged_error = pub.loggederror_class.select()[0]
     assert logged_error.formdef_id == formdef.id
-    assert logged_error.summary == 'Failed to set value on field "file"'
-    assert logged_error.exception_class == 'AttributeError'
-    assert logged_error.exception_message == "'str' object has no attribute 'time'"
+    assert logged_error.summary == 'Failed to convert value for field "file"'
+    assert logged_error.exception_class == 'ValueError'
+    assert logged_error.exception_message == "invalid data for file type ('foo bar wrong value')"
 
 
 def test_form_file_field_prefill(pub):