Import: Parse iso dates

src/pretix/base/modelimport.py

@@ -213,7 +213,13 @@ class DatetimeColumnMixin:
             except (ValueError, TypeError):
                 pass
         else:
-            raise ValidationError(_("Could not parse {value} as a date and time.").format(value=value))
+            try:
+                d = datetime.datetime.fromisoformat(value)
+                if not d.tzinfo:
+                    d = d.replace(tzinfo=self.timezone)
+                return d
+            except (ValueError, TypeError):
+                raise ValidationError(_("Could not parse {value} as a date and time.").format(value=value))
 
 
 class DecimalColumnMixin:

src/tests/base/test_modelimport_vouchers.py

@@ -66,7 +66,7 @@ def inputfile_factory(multiplier=1):
             'A': 'GHIJK432',
             'B': 'Ticket',
             'C': 'False',
-            'D': '2021-05-28 11:00:00',
+            'D': '2021-05-28T11:00:00+00:00',
             'E': '2',
             'F': '1',
         },