Allow specifying max heap size from env #13

Job	Run time
ci / Build	5m 40s
ci / Lint	1m 7s
ci / Test (0)	7m 17s
ci / Test (1)	6m 16s
ci / Test (2)	5m 42s
ci / Test (3)	9m 26s
ci / Test (4)	7m 56s
ci / Test (5)	4m 47s
ci / Test (6)	5m 3s
ci / Test (7)	7m 19s
ci / Test (8)	4m 12s
ci / Test (9)	6m 20s
ci / Publish Unit Tests Results	1s
	1h 11m 6s

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