Allow specifying max heap size from env #15

Job	Run time
ci / Build	6m 2s
ci / Lint	1m 20s
ci / Test (0)	7m 51s
ci / Test (1)	5m 16s
ci / Test (2)	5m 10s
ci / Test (3)	7m 49s
ci / Test (4)	8m 7s
ci / Test (5)	22m 27s
ci / Test (6)	7m 4s
ci / Test (7)	4m 57s
ci / Test (8)	5m 14s
ci / Test (9)	6m 22s
ci / Publish Unit Tests Results	1s
	1h 27m 40s

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