ci: integration tests against multiple juju versions #1085

Job	Run time
Build test (3.10)	22s
Validate (3.10)	23s
Linter (3.9)	12s
Linter (3.10)	11s
Unit tests (3.8)	24s
Unit tests (3.9)	32s
Unit tests (3.10)	26s
Unit tests (3.11)	24s
Unit tests (3.12)	31s
Unit tests (3.13)	38s
Integration (3.10, 3.1/stable)	46m 31s
Quarantined Integration Tests (3.10, 3.1/stable)	50m 15s
Integration (3.10, 3.3/stable)	48m 59s
Quarantined Integration Tests (3.10, 3.3/stable)	44m 42s
Integration (3.10, 3.4/stable)	45m 45s
Quarantined Integration Tests (3.10, 3.4/stable)	1h 11m 19s
Integration (3.10, 3.5/stable)	42m 20s
Quarantined Integration Tests (3.10, 3.5/stable)	55m 55s
	6h 49m 49s

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