Problems with Oracle 21 (behat testing failures)

This is a continuation of MDL-75208, where some PHPUnit failures with Oracle 21 were fixed (workaround).

As reported originally the Oracle 21c image is noticeably slower (~25%) than then 11g and that has caused various Behat tests to start failing often.

Some are old randoms that were improved in the past, other are new scenarios not failing earlier.

Here there is a reference run (note that the failures can change, we'll try to collect the more common ones in this issue):

• Behat (non-js): https://ci.moodle.org/view/Testing/job/DEV.01%20-%20Developer-requested%20Behat/25247/
• Behat (js): https://ci.moodle.org/view/Testing/job/DEV.01%20-%20Developer-requested%20Behat/25246/

This issue is about to try to minimize the impact of those failues, of course reviewing all them in case they are new to verify that the problem is purely a slow one.

Together, some improvements will be tried with the 21c image to see if it can be done to perform better.