Add option to disable artifact upload in checkout-junit-reports sub-a… #73

Job	Run time
Checkout JUnit reports	24s
Generate split indexes	2s
Test #0	48s
Test #1	32s
Test #2	40s
Test #3	35s
Merge JUnit reports with existing branch	23s
Merge JUnit reports with new branch	27s
	3m 51s

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