feat(spring): enable `openApiNullable` with `useJackson3` #3016

Job	Run time
Gradle tests (samples/openapi3/client/extensions/x-auth-id-alias/java/jersey2-java8)	1m 23s
Gradle tests (samples/openapi3/client/petstore/java/jersey2-java8-special-characters)	1m 28s
Gradle tests (samples/client/petstore/java/okhttp-gson)	1m 26s
Gradle tests (samples/client/petstore/java/native)	1m 24s
Gradle tests (samples/client/petstore/java/jersey2-java8-localdatetime)	1m 28s
Gradle tests (samples/openapi3/client/petstore/java/jersey2-java8)	1m 31s
Gradle tests (samples/client/petstore/java/webclient-swagger2)	1m 32s
Gradle tests (samples/client/petstore/java/native-jakarta)	1m 17s
Gradle tests (samples/client/petstore/java/okhttp-gson-group-parameter)	1m 17s
Gradle tests (samples/client/petstore/java/jersey2-java8)	1m 20s
	14m 6s

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