Fix missing repo link in issue/pull assigned emails (#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 locale string.

Fix #17160

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>

services/mailer/mail.go

@@ -372,6 +372,12 @@ func SendIssueAssignedMail(issue *models.Issue, doer *models.User, content strin
 		// No mail service configured
 		return nil
 	}
+
+	if err := issue.LoadRepo(); err != nil {
+		log.Error("Unable to load repo [%d] for issue #%d [%d]. Error: %v", issue.RepoID, issue.Index, issue.ID, err)
+		return err
+	}
+
 	langMap := make(map[string][]*models.User)
 	for _, user := range recipients {
 		langMap[user.Language] = append(langMap[user.Language], user)