deps: update dependency platformdirs to v4.2.1 #6500

Job	Run time
build (11)	12m 29s
build(8) except for gapic-generator-java	4m 7s
build(21) except self-service clients	11m 39s
build (17)	12m 21s
build(8) for gapic-generator-java	9m 30s
lint	20s
compatibility	1m 25s
dependency_analyzer_unit_test	12s
gapic-generator-java-bom	1m 48s
showcase (11)	4m 0s
showcase (17)	3m 54s
showcase-clirr	2m 59s
showcase-native	8m 24s
unmanaged_dependency_check	5m 52s
	1h 19m 0s

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