[DPE-4976] Add workflow for nightly scheduled tests with juju 3.6 #4

Job	Run time
Lint / tox run -e lint	19s
Lint / Lint .github/workflows/	3s
Build charm / Collect bases for charm \| .	21s
Build charm / Build charm \| base #0	7m 37s
Build charm / Build charm \| base #1	9m 48s
Integration \| 3.6 / 3.6/beta \| amd64 \| Collect integration test groups	31s
Integration \| 3.6 / high_availability/test_async_replication.py \| group 1	35m 30s
Integration \| 3.6 / high_availability/test_replication.py \| group 1	20m 58s
Integration \| 3.6 / high_availability/test_replication.py \| group 2	18m 2s
Integration \| 3.6 / high_availability/test_replication.py \| group 3	24m 32s
Integration \| 3.6 / high_availability/test_self_healing.py \| group 1	27m 24s
Integration \| 3.6 / high_availability/test_upgrade.py \| group 1	7m 6s
Integration \| 3.6 / high_availability/test_upgrade_from_stable.py \| group 1	6m 18s
Integration \| 3.6 / high_availability/test_upgrade_rollback_incompat.py \| group 1	14m 36s
Integration \| 3.6 / relations/test_database.py \| group 1	11m 44s
Integration \| 3.6 / relations/test_db_router.py \| group 1	43m 43s
Integration \| 3.6 / relations/test_relation_mysql_legacy.py \| group 1	4m 34s
Integration \| 3.6 / relations/test_shared_db.py \| group 1	30m 24s
Integration \| 3.6 / test_backup_aws.py \| group 1	23m 33s
Integration \| 3.6 / test_backup_ceph.py \| group 1	30m 33s
Integration \| 3.6 / test_backup_gcp.py \| group 1	29m 48s
Integration \| 3.6 / test_subordinate_charms.py \| group 1	13m 34s
Integration \| 3.6 / test_tls.py \| group 1	22m 32s
Integration \| 3.6 / (beta) Publish Allure report	0s
	6h 23m 30s

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