deps: update dependency lxml to v5.2.1 #6185

Job	Run time
build (11)	12m 34s
build(21) except self-service clients	11m 9s
build (17)	12m 12s
build(8) except for gapic-generator-java	3m 45s
build(8) for gapic-generator-java	9m 29s
gapic-generator-java-bom	1m 49s
compatibility	1m 27s
lint	24s
showcase (11)	4m 3s
showcase (17)	4m 9s
showcase-clirr	2m 54s
unmanaged_dependency_check	3m 46s
showcase-native	8m 7s
dependency_analyzer_unit_test	13s
	1h 16m 1s

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