Add support for checking out non-existent branches in JUnit reports w… #118

Job	Run time
Checkout JUnit reports	22s
Checkout JUnit reports with non-existent branch	5s
Generate split indexes	5s
Test #2	1m 0s
Test #0	59s
Test #3	1m 1s
Test #1	1m 3s
Merge JUnit reports with existing branch	39s
Merge JUnit reports with new branch	28s
	5m 42s

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