ci: increase graalvm ci machine type (#2760) #6628

Job	Run time
build(21) except self-service clients	55s
build (11)	12m 23s
build (17)	12m 27s
compatibility	1m 32s
build(8) for gapic-generator-java	9m 15s
build(8) except for gapic-generator-java	3m 56s
gapic-generator-java-bom	1m 41s
lint	24s
showcase-native	8m 27s
showcase (11)	3m 53s
showcase (17)	4m 3s
dependency_analyzer_unit_test	19s
showcase-clirr	0s
unmanaged_dependency_check	4m 34s
	1h 3m 49s

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