version = 2021052500 release version
requires= 2021052500 same than version

Why 20210525? (25th May 2021) ?

Because master is going to be Moodle 4.0, to be released
on November 2021. And, until then, we are going to have
a couple of "intermediate" releases:

- Moodle 3.10 to be released 9th November 2020. (2020110900)

  This version will be using versions from today to 2020110900
  (once it's released the YYYYMMDD part stops advancing).

- Moodle 3.11 to be released 10th May 2021. (2021051000)

  This version will be using versions from 3.10 release to 2021051000
  (once it's released the YYYYMMDD part stops advancing).

That means that all versions from today to 2021051000 are going
to be used by those 2 "intermediate" releases (3.10 and 3.11).

And we cannot use them in master, because it's forbidden to have
any overlapping of versions between branches (or different upgrade
paths will fail).

So, get that 2021051000, let's add it a couple of weeks to cover
the on-sync period (or a 2 weeks delay max!) and, the first version
that master can "own" in exclusive (without any overlap) is, exactly,
25th May 2021, hence our 20210525.