MDL-77429 course: Change course date to previous day

When a test runs just after midnight, and the user time zone is not the
same as the server timezone, and the course is created using a generator
(which runs in server time zone) but the UI presented in the user
timezone, the course start time is still in the future.

We need to create the course a day earlier to ensure that the "This
week" indicator is in the correct day.

course/tests/behat/course_format.feature

@@ -11,8 +11,8 @@ Feature: Teacher can change the course format
       | teacher1 | Teacher   | 1        | teacher1@example.com |
     # Course format is initially set to Topics format
     And the following "courses" exist:
-      | fullname | shortname | format |
-      | Course 1 | C1        | topics |
+      | fullname | shortname | format | startdate       |
+      | Course 1 | C1        | topics | ## 1 day ago ## |
     And the following "course enrolments" exist:
       | user     | course | role           |
       | teacher1 | C1     | editingteacher |