Fix: notify locale on reassigned issueable email

What does this MR do and why?

Fix the un-translated hardcoded string in the email template for reassigned issuable.

I think keeping these strings segmented is a better way than merging them into a gigantic string with conditions.

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app/views/notify/_reassigned_issuable_email.html.haml

-- to_names = content_tag(:strong, issuable.assignees.any? ? sanitize_name(issuable.assignee_list) : s_('Unassigned')).html_safe
+- to_names = content_tag(:strong, issuable.assignees.any? ? sanitize_name(issuable.assignee_list) : s_('Unassigned'))
 
 %p
   - if previous_assignees.any?
-    = html_escape(s_('Notify|Assginee changed from %{fromNames} to %{toNames}').html_safe % { fromNames: content_tag(:strong, sanitize_name(previous_assignees.map(&:name).to_sentence)), toNames: to_names })
+    = html_escape(s_('Notify|Assignee changed from %{fromNames} to %{toNames}').html_safe % { fromNames: content_tag(:strong, sanitize_name(previous_assignees.map(&:name).to_sentence)), toNames: to_names })
   - else
-    = html_escape(s_('Notify|Assginee changed to %{toNames}').html_safe % { toNames: to_names})
+    = html_escape(s_('Notify|Assignee changed to %{toNames}').html_safe % { toNames: to_names})