Little discrepancies found between 310 and master

While performing some routine checks, it has been detected that there are, right now, a few differences between 310_STABLE and master that shouldn't be there.

Note that this is only for these 2 branches, because they haven't diverged (other than version numbers). In the future, once diverged, this check won't be useful ever.

This is the (one-liner) check:

git diff MOODLE_310_STABLE master --stat | grep -v version.php | grep -v install/lang | grep -v 'files changed' | cut -d' ' -f2 | xargs git diff MOODLE_310_STABLE master

And, inspecting the differences, after discarding all being just version / branch numbers, there are 3 cases that need to be verified and, if possible, fixed:

1. lib/db/upgrade.php : There is an upgrade step that, for some reason seems to be in different order between the 2 branches. Worth checking it and see why that is happening.
2. lib/phpunit/classes/phpunit_dataset.php : There is a phpdoc @param wrong in master (from_string() method.
3. theme/boost/scss/moodle/core.scss : There is a discrepancy with one of the selectors (movehere).

So this issue is about to examine those 3 changes and proceed to reconcile both branches (version numbers aside) so they look the same.

Ciao