feat(spring): enable `openApiNullable` with `useJackson3` #66

Job	Run time
Build Java Spring (JDK17) (samples/openapi3/server/petstore/springboot-4)	49s
Build Java Spring (JDK17) (samples/server/petstore/springboot-api-response-examples)	46s
Build Java Spring (JDK17) (samples/openapi3/server/petstore/springboot-3)	52s
Build Java Spring (JDK17) (samples/client/petstore/spring-http-interface-springboot-4)	41s
Build Java Spring (JDK17) (samples/server/petstore/springboot-lombok-tostring)	44s
Build Java Spring (JDK17) (samples/server/petstore/springboot-lombok-data)	55s
Build Java Spring (JDK17) (samples/openapi3/client/petstore/spring-cloud-3-with-optional)	41s
Build Java Spring (JDK17) (samples/openapi3/server/petstore/spring-boot-oneof-interface)	53s
Build Java Spring (JDK17) (samples/openapi3/server/petstore/spring-boot-oneof-sealed)	45s
Build Java Spring (JDK17) (samples/openapi3/client/petstore/spring-cloud-4-with-optional)	53s
Build Java Spring (JDK17) (samples/server/petstore/springboot-file-delegate-optional)	48s
Build Java Spring (JDK17) (samples/server/petstore/springboot-petstore-with-api-response-examples)	52s
	9m 39s

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