Fix: locale on new ssh key email

What does this MR do and why?

Reason

The current version of new ssh key email is not using translated strings to the user. This MR is meant to fix that.

Describe in detail what your merge request does and why.

Screenshots or screen recordings

Before

After

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

1. Boot GDK
2. Go to user preference settings > SSH Keys
3. Add a new SSH key
4. Go to gdk_host/rails/letter_opener to see the mail preview

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.