Fix constant within tests.

Author: desrosj

tests/phpunit/tests/functions.php

@@ -1573,7 +1573,7 @@ public function test_wp_getimagesize_heic() {
 		$expected = array(
 			1180,
 			1180,
-			IMAGETYPE_HEIC,
+			IMAGETYPE_HEIF,
 			'width="1180" height="1180"',
 		);