org-file-tags: not updated with org-ql searches

Contrary to the how org-agenda works, org-ql do not update org-file-tags variable. It looks like that org-agenda updating org-file-tags variable in `org-agenda-prepare-buffers` function (or more specifically `(org-set-regexps-and-options 'tags-only)`).

They are called in org-agenda-redo, but when tried to do agenda redo with org-ql it didn't update me file tags variable.

I'm not sure if it became broken or always been broken. Last time we were dealing with file tags, I thought that this is just effect of caching and dismissed these problems.

Possibly instead of relying on org-file-tags variable and fragile org-agenda-mode API, org-ql should read these variables on its own.