ci(spanner): Enable directpath in Kokoko jobs #10630

Job	Run time
units (11)	3m 0s
units-with-multiplexed-session (11)	3m 23s
units (8)	3m 7s
units (17)	2m 54s
units-with-multiplexed-session (17)	3m 9s
units (21)	3m 4s
units-with-multiplexed-session (21)	3m 19s
dependencies (17)	1m 19s
clirr	1m 8s
javadoc	2m 43s
lint	1m 11s
units-with-multiplexed-session (8)	3m 47s
windows	7m 50s
	39m 54s

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