Increase CanValidateDateTimeTest invalid data test coverage

This change is to ensure `Respect\Validation` is intentional about the
DateTime formats.

For context the [ISO 8601][] standard says that we shouldn't accept
`-00:00` (or anything similar) offsets.

I noticed that there was an a [change][] in how
`CanValidateDateTime.php` behaved from v2.2 to v2.3.

Prior to v2.3 date time formats of `2018-01-30T19:04:35-00:00` (note the
-00:00) would pass validation. After updating to v2.3 the format is not
accepted.

This is because the `DateTime::createFromFormat` accepts the `$value`
of `2018-01-30T19:04:35-00:00` but internally converts the `-00:00` to
`+00:00`

```
$formattedDate = DateTime::createFromFormat(
    $format,
    $value,
    new DateTimeZone(date_default_timezone_get())
);
```

This in turn causes the validation around
`$value !== $formattedDate->format($format))` to fail

```
if ($formattedDate === false || $value !== $formattedDate->format($format)) {
    return false;
}
```

[ISO 8601]: https://en.wikipedia.org/wiki/ISO_8601#Other_time_offset_specifications
[change]: 5fe4b96

Author: agchan12

tests/unit/Helpers/CanValidateDateTimeTest.php

@@ -64,6 +64,10 @@ public static function providerForInvalidDateTime(): array
             ['Y-m-d', '0000-00-31'],
             ['Y-m-d', '0000-12-00'],
             ['Y-m-d H:i:s', '1987-12-31'],
+            ['c', '2018-01-30T19:04:35-00:00'],
+            ['Y-m-d\TH:i:sP', '2018-01-30T19:04:35-00:00'],
+            ['r', 'Tue, 30 Jan 2018 19:06:01 -0000'],
+            ['D, d M Y H:i:s O', 'Tue, 30 Jan 2018 19:06:01 -0000'],
         ];
     }
 }