Bug 1661434 - Add tring to the codespell exclude list

In the doc, we have an example of a regex called
[s]tring
it is confusing for codespell

Differential Revision: https://phabricator.services.mozilla.com/D88806

tools/lint/spell/exclude-list.txt

@@ -13,3 +13,5 @@ thru
 referer
 dur
 ue
+tring
+