Makefile: Use Maven verify goal instead of integration-test

We shouldn't be using the `integration-test` goal directly because:

* It doesn't check the results of the tests, meaning the build succeeds
  even if the tests fail
* The post-integration-test phase, which tears down the test
  environment, doesn't run

https://maven.apache.org/surefire/maven-failsafe-plugin/index.html

Makefile

@@ -18,7 +18,7 @@ test: ## Run tests
 
 .PHONY: integration-test
 integration-test: ## Run integration tests
-	mvn --batch-mode clean integration-test
+	mvn --batch-mode clean verify -Dgpg.skip
 
 .PHONY: bootstrap-with-docker
 bootstrap-with-docker: ## Prepare the Docker builder image