Fix test coverage #6388

Job	Run time
Build Ballerina Lang	3m 50s
Build Ballerina Distribution	40m 9s
Build Stdlib Level (1)	5m 55s
Build Stdlib Level (2)	13m 40s
Build Stdlib Level (3)	8m 3s
Build Stdlib Level (4)	15m 13s
Build Stdlib Level (5)	35m 23s
Build Stdlib Level (6)	21m 10s
Build Stdlib Level (7)	17m 55s
Build Stdlib Level (8)	37m 48s
Build Stdlib Level (9)	4m 52s
	3h 23m 58s

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