Upgrade to JUnit 5.3.1

pom.xml

spring-petclinic-api-gateway/pom.xml

...ork/samples/petclinic/api/ApiGatewayApplicationTests.java

spring-petclinic-config-server/pom.xml

...tclinic/config/PetclinicConfigServerApplicationTests.java

spring-petclinic-customers-service/pom.xml

...ples/petclinic/customers/web/PetResourceDatabaseTest.java

...work/samples/petclinic/customers/web/PetResourceTest.java

spring-petclinic-discovery-server/pom.xml

.../petclinic/discovery/DiscoveryServerApplicationTests.java

spring-petclinic-tracing-server/pom.xml

spring-petclinic-vets-service/pom.xml

...k/samples/petclinic/vets/web/VetResourceDatabaseTest.java

...framework/samples/petclinic/vets/web/VetResourceTest.java

spring-petclinic-visits-service/pom.xml

...k/samples/petclinic/visits/VisitResourceDatabaseTest.java

...ework/samples/petclinic/visits/web/VisitResourceTest.java