[EE] Fix a potential frozen string error in app/mailers/notify.rb and add tests for Service desk emails
requested to merge ee-55183-frozenerror-can-t-modify-frozen-string-in-app-mailers-notify-rb into master
EE port of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23728.
What does this MR do?
Normally, we won't hit frozen string error since callers of Notify#mail_answer_note_thread alls call Notify#subject to generate the subject, which returns a non-frozen string.
That said, better be safe we had a case where Service Desk emails weren't using Notify#subject to generate the subject and thus hitting the frozen string error when calling Notify#mail_answer_thread (https://gitlab.com/gitlab-org/gitlab-ce/issues/55104 => https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23683).
What are the relevant issue numbers?
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/55104.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/55183.
Does this MR meet the acceptance criteria?
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Changelog entry added, if necessary - [-] Documentation created/updated
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Tests added for this feature/bug -
Conforms to the code review guidelines -
Conforms to the merge request performance guidelines -
Conforms to the style guides -
Conforms to the database guides - [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
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EE specific content should be in the top level /eefolder - [-] For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
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Security reports checked/validated by reviewer
Edited by Rémy Coutable