MDL-75889 core: compare domain names in a case-insensitive manner.

As per https://www.rfc-editor.org/rfc/rfc1035#section-3.1

lib/tests/ip_utils_test.php

@@ -14,13 +14,13 @@
 // You should have received a copy of the GNU General Public License
 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 
-
 namespace core;
 
 /**
  * This tests the static helper functions contained in the class '\core\ip_utils'.
  *
  * @package    core
+ * @covers     \core\ip_utils
  * @copyright  2016 Jake Dallimore <[email protected]>
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
@@ -355,6 +355,7 @@ class ip_utils_test extends \basic_testcase {
     public function data_domain_addresses() {
         return [
             [true, 'example.com'],
+            [true, 'ExAmPle.com'],
             [false, 'sub.example.com'],
             [false, 'example.com.au'],
             [false, ' example.com'], // A space at the front of the domain is invalid.
@@ -362,6 +363,8 @@ class ip_utils_test extends \basic_testcase {
             [false, 'test.example.com'],
             [false, 'moodle.com'],
             [true, 'test.moodle.com'],
+            [true, 'TeSt.moodle.com'],
+            [true, 'test.MoOdLe.com'],
             [false, 'test.moodle.com.au'],
             [true, 'nice.address.per.this.penny-arcade.com'],
             [false, 'normal.per.this.penny-arcade.com.au'],