Open CSV export file using with newline translation

The csv documentation [1] explains that file object used in writer should be
opened with newline as empty string.

[1] https://docs.python.org/3/library/csv.html

Closes #12115
(grafted from c07aae86c7fe87715994f0e82177980b9907dc3f)

--HG--
branch : 6.0

tryton/tryton/gui/window/form.py

@@ -458,7 +458,7 @@ class Form(SignalEvent, TabContent):
             delimiter = ';'
         fileno, fname = tempfile.mkstemp(
             '.csv', common.slugify(export['name']) + '_')
-        with open(fname, 'w') as fp:
+        with open(fname, 'w', newline='') as fp:
             writer = csv.writer(fp, delimiter=delimiter)
             writer.writerow(fields)
             for row, path in zip_longest(data, paths or []):