bump version to 5.0.0 #308

Job	Run time
define-matrix	3s
test (8.3, main, pgsql, true)	1m 12s
test (8.3, main, mariadb, true)	3m 20s
test (8.1, MOODLE_404_STABLE, pgsql, false)	3m 29s
test (8.1, MOODLE_404_STABLE, mariadb, false)	3m 21s
test (8.2, MOODLE_404_STABLE, pgsql, false)	3m 37s
test (8.2, MOODLE_404_STABLE, mariadb, false)	3m 20s
test (8.3, MOODLE_404_STABLE, pgsql, false)	3m 25s
test (8.3, MOODLE_404_STABLE, mariadb, false)	3m 39s
test (8.1, MOODLE_405_STABLE, pgsql, false)	3m 38s
test (8.1, MOODLE_405_STABLE, mariadb, false)	3m 32s
test (8.2, MOODLE_405_STABLE, pgsql, false)	3m 27s
test (8.2, MOODLE_405_STABLE, mariadb, false)	3m 49s
test (8.3, MOODLE_405_STABLE, pgsql, false)	3m 24s
test (8.3, MOODLE_405_STABLE, mariadb, false)	3m 35s
	46m 51s

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