issue #3: add persistent classes #7

Job	Run time
ci / check if job needs to run	4s
ci / prepare test matrix	13s
ci / MOODLE_401_STABLE - pgsql - php 8.0 - tool_dynamic_cohorts	2m 13s
ci / MOODLE_401_STABLE - pgsql - php 7.4 - tool_dynamic_cohorts	1m 20s
ci / MOODLE_401_STABLE - mariadb - php 7.4 - tool_dynamic_cohorts	1m 25s
ci / MOODLE_401_STABLE - mariadb - php 8.0 - tool_dynamic_cohorts	1m 48s
ci / MOODLE_402_STABLE - pgsql - php 8.0 - tool_dynamic_cohorts	2m 5s
ci / MOODLE_402_STABLE - mariadb - php 8.0 - tool_dynamic_cohorts	1m 36s
ci / MOODLE_402_STABLE - pgsql - php 8.1 - tool_dynamic_cohorts	1m 56s
ci / MOODLE_402_STABLE - mariadb - php 8.1 - tool_dynamic_cohorts	2m 8s
ci / MOODLE_403_STABLE - pgsql - php 8.0 - tool_dynamic_cohorts	2m 9s
ci / MOODLE_403_STABLE - mariadb - php 8.0 - tool_dynamic_cohorts	1m 30s
ci / MOODLE_403_STABLE - pgsql - php 8.2 - tool_dynamic_cohorts	2m 21s
ci / MOODLE_403_STABLE - mariadb - php 8.2 - tool_dynamic_cohorts	1m 57s
ci / Release to the Moodle plugin directory	0s
	22m 45s

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