MDL-72428 lang: Use the fixed strings in the tests

mod/forum/tests/behat/inpage_reply.feature

@@ -42,6 +42,6 @@ Feature: Students can reply to a discussion in page.
       | post | Discussion contents 1, third message |
       | privatereply | 1                            |
     Then I should see "Discussion contents 1, third message"
-    Then I should see "This is a private reply. It is not visible to other participants."
+    Then I should see "This is a private reply. It is only visible to you and anyone with the capability to view private replies, such as teachers or managers."
     When I reload the page
     Then I should see "Discussion contents 1, third message"