ci: update showcase tests and build java tests to JDK 25 #11949

Job	Run time
build (11)	14m 51s
build(21) except self-service clients	13m 43s
build(25) except self-service clients	12m 49s
build (17)	15m 4s
build(8) except for gapic-generator-java	5m 16s
showcase (25)	11m 1s
build(8) for gapic-generator-java	11m 10s
compatibility	2m 24s
unmanaged_dependency_check	9m 51s
dependency_analyzer_unit_test	28s
showcase (11)	10m 49s
showcase (17)	10m 56s
gapic-generator-java-bom	2m 44s
showcase-clirr	4m 4s
lint	1m 3s
showcase (21)	11m 36s
build(8) for showcase	5m 8s
	2h 22m 57s

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