feat(auth): add JSpecify Null annotations to Auth #5374

Job	Run time
filter	1m 12s
sdk-platform-java integration (11)	8m 13s
gapic-generator-java (8)	12m 3s
sdk-platform-java self-service clients (17)	9m 39s
sdk-platform-java integration (JDK 24+) (25)	11m 5s
unmanaged_dependency_check	12m 15s
sdk-platform-java integration (21)	10m 44s
dependency_analyzer_unit_test	1m 27s
dependencies	3m 29s
gapic-generator-java-bom	3m 32s
sdk-platform-java integration (17)	11m 8s
clirr	3m 56s
sdk-platform-java integration (JDK 24+) (26)	10m 7s
sdk-platform-java self-service clients (11)	9m 34s
sdk-platform-java units (11)	4m 51s
sdk-platform-java units (21)	5m 5s
sdk-platform-java units (25)	4m 30s
java8-compatibility	6m 22s
sdk-platform-java units (8)	3m 17s
sdk-platform-java units (26)	5m 12s
sdk-platform-java units (17)	4m 30s
	2h 22m 11s

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