Add MOODLE_403_STABLE GHA tests #533

Job	Run time
Code coverage (codecov)	0s
CI test (make validate)	52s
Build moodle-plugin-ci.phar	43s
Integration tests (8.2, master)	8m 16s
Integration tests (8.2, MOODLE_403_STABLE)	7m 56s
Integration tests (8.2, MOODLE_402_STABLE)	7m 24s
Integration tests (8.1, MOODLE_401_STABLE)	7m 10s
Integration tests (8.0, MOODLE_400_STABLE)	8m 19s
Integration tests (8.0, MOODLE_311_STABLE)	8m 21s
Integration tests (7.4, MOODLE_310_STABLE)	6m 2s
Integration tests (7.4, MOODLE_39_STABLE)	7m 49s
Integration tests (7.4, MOODLE_38_STABLE)	7m 23s
Integration tests (PHAR) (8.2, master)	7m 10s
Integration tests (PHAR) (8.1, MOODLE_403_STABLE)	6m 54s
Integration tests (PHAR) (8.0, MOODLE_401_STABLE)	7m 2s
Integration tests (PHAR) (7.4, MOODLE_400_STABLE)	6m 11s
	1h 37m 32s

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