Fix missing repo link in issue/pull assigned emails (#17183) (#17184)

Backport #17183

There was a mistake in the template file: `templates/mail/issue/assigned.tmpl`
where the repourl was generated from a non-existent release instead of the issue.

This PR changes this to use the issue but also ensure that the issue repo is loaded.

It also slightly improves the English and the Russian locale string.

Fix #17160

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>

templates/mail/issue/assigned.tmpl

@@ -8,7 +8,7 @@
 	<title>{{.Subject}}</title>
 </head>
 
-{{$repo_url := printf "<a href='%s'>%s</a>" .Release.Repo.HTMLURL .Release.Repo.FullName}}
+{{$repo_url := printf "<a href='%s'>%s</a>" .Issue.Repo.HTMLURL .Issue.Repo.FullName}}
 {{$link := printf "<a href='%s'>#%d</a>" .Link .Issue.Index}}
 <body>
 	<p>