Bump actions/checkout from 3 to 6 (#962) #76

Job	Run time
deploy / setup	5s
deploy / Build 3.3.x (JDK 25)	5m 18s
deploy / Build 3.3.x (JDK 17)	6m 24s
deploy / Build 3.3.x (JDK 21)	9m 5s
deploy / Trigger CI for non-default branches	0s
	20m 52s

Provide feedback