Older PHP versions set SameSite attribute on insecure session cookie

MR is not mergeable anymore, as there were recent changes in drupal_setcookie() function.

Thanks for working on this. I have tested this on PHP 8.1 and if I set $conf['https'] = TRUE;, $conf['samesite_cookie_value'] = 'None'; and login via HTTPS, my Chrome browser still complains about the insecure session cookie with SameSite attribute. Does this problem really affect only PHP versions earlier than 7.3?

Cookies with SameSite attribute are tested heavily in SessionTestCase and I think we should add a test for this - just to check if the SameSite attribute is present only in the secure cookie. See the uploaded test-only patch. I have not tested that patch on all PHP/SSL combinations.

I have added this issue to the list of potential candidates for the next release - but we need to verify the point raised in #7 and add a test, so that we can compare test-only and regular patch results to see PHP versions affected by this (and confirm that the patch is correct). Thanks!