feat(auth): add JSpecify Null annotations to Auth #5424

Job	Run time
filter	1m 12s
gapic-generator-java (8)	9m 6s
sdk-platform-java integration (JDK 24+) (25)	9m 34s
sdk-platform-java units (8)	4m 31s
gapic-generator-java-bom	3m 18s
sdk-platform-java integration (JDK 24+) (26)	10m 50s
sdk-platform-java integration (21)	3m 14s
sdk-platform-java integration (11)	2m 57s
clirr	3m 18s
sdk-platform-java integration (17)	2m 57s
java8-compatibility	5m 15s
sdk-platform-java self-service clients (11)	9m 41s
dependency_analyzer_unit_test	1m 29s
sdk-platform-java units (25)	3m 34s
unmanaged_dependency_check	12m 31s
sdk-platform-java units (26)	4m 18s
sdk-platform-java units (11)	4m 44s
sdk-platform-java units (17)	5m 6s
sdk-platform-java self-service clients (17)	9m 2s
sdk-platform-java units (21)	4m 6s
dependencies	3m 54s
	1h 54m 37s

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