Limit stylelint tasks to plugin directory #661

Job	Run time
CI test (make validate)	56s
Code coverage (codecov)	53s
Build moodle-plugin-ci.phar	38s
Integration tests (8.3, main)	7m 7s
Integration tests (8.3, MOODLE_404_STABLE)	6m 41s
Integration tests (8.2, MOODLE_403_STABLE)	6m 18s
Integration tests (8.2, MOODLE_402_STABLE)	6m 31s
Integration tests (8.1, MOODLE_401_STABLE)	6m 38s
Integration tests (8.0, MOODLE_400_STABLE)	6m 54s
Integration tests (8.0, MOODLE_311_STABLE)	5m 56s
Integration tests (7.4, MOODLE_39_STABLE)	5m 35s
Integration tests (PHAR) (8.3, main)	6m 49s
SelfUpdate tests (PHAR) (8.3)	1m 26s
Integration tests (PHAR) (8.3, MOODLE_404_STABLE)	6m 14s
SelfUpdate tests (PHAR) (8.2)	44s
Integration tests (PHAR) (8.2, MOODLE_403_STABLE)	5m 45s
SelfUpdate tests (PHAR) (8.1)	26s
Integration tests (PHAR) (8.1, MOODLE_402_STABLE)	5m 34s
SelfUpdate tests (PHAR) (8.0)	28s
Integration tests (PHAR) (8.0, MOODLE_401_STABLE)	6m 10s
SelfUpdate tests (PHAR) (7.4)	46s
Integration tests (PHAR) (7.4, MOODLE_400_STABLE)	5m 37s
	1h 34m 6s

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