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.

Describe in detail what your merge request does and why.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

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

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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

app/views/notify/_reassigned_issuable_email.html.haml

 %p
   = _('Notify|Assignee changed')
   - if previous_assignees.any?
-    - # The reason we put namespace here is that 'from' and 'to' could be translated
-    - # into different meanings in different context, for instance Chinese.
+    -# The reason we put namespace here is that 'from' and 'to' could be translated
+    -# into different meanings in different context, for instance Chinese.
     = _("Notify|from")
     %strong= sanitize_name(previous_assignees.map(&:name).to_sentence)
   = _('Notify|to')