Make "Update Tag Filters" troubleshooting option work for unfilterable tags
Description
The "Update Tag Filters" troubleshooting option (available only to admins) uses Tag#synonyms, which generates an error if the tag is not canonical and doesn't have a merger. It should use Tag#mergers instead, to make sure that it works for all tags.
Testing Instructions
Log in as admin.
Find a tag that's not canonical and has no synonym set.
Go to the tag's Troubleshoot page.
Check the "Update Tag Filters" option.
Press "Troubleshoot."
Make sure that it returns a success notice, instead of a 500 error.
Activity
For the next tester use
went to https://test.archiveofourown.org/tags/High High High - Fandom pressed troubleshoot
Clicked all the buttons, seemed happy
Looks good to me
I tested using the tag ‘DVR’ which didn’t appear to have any syns and didn’t seem to be Canonical. After following the steps, it successfully returned “Tagged items enqueued for filter updates.” instead of a 500 error.
