MDL-72605 my: Fix behat error with classic

This is a regression caused by MDL-72116, where the "Upcoming events"
block was removed from the dashboard.
In classic is failing because the text "Upcoming events" is displayed
in the "Add a block" list. So stopping edition should fix the issue.

my/tests/behat/add_blocks.feature

@@ -21,6 +21,7 @@ Feature: Add blocks to dashboard page
   Scenario: Add blocks to page
     When I press "Customise this page"
     And I add the "Latest announcements" block
+    And I press "Stop customising this page"
     Then I should see "Latest announcements" in the "Latest announcements" "block"
     And I should see "Latest badges" in the "Latest badges" "block"
     And I should see "Calendar" in the "Calendar" "block"