General: Continuing to work towards a passing PHP Compatibility scan.

- Add `phpcs:ignore` statements to compatibility checks in PHPMailer.
- Remove quotes around the assertion in an `assert()` call. This will trigger a deprecated notice under certain conditions on PHP 7.2.

Props jrf, desrosj.
See #49922, #48033.

git-svn-id: https://develop.svn.wordpress.org/trunk@48045 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/Text/Diff/Engine/shell.php

@@ -83,7 +83,7 @@ class Text_Diff_Engine_shell {
 
             if ($from_line_no < $match[1] || $to_line_no < $match[4]) {
                 // copied lines
-                assert('$match[1] - $from_line_no == $match[4] - $to_line_no');
+                assert($match[1] - $from_line_no == $match[4] - $to_line_no);
                 array_push($edits,
                     new Text_Diff_Op_copy(
                         $this->_getLines($from_lines, $from_line_no, $match[1] - 1),