Make milestone plugin dependencies available to Maven integration tests

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/projects/settings.xml

@@ -45,6 +45,11 @@
 					</snapshots>
 					<checksumPolicy>ignore</checksumPolicy>
 				</pluginRepository>
+				<pluginRepository>
+					<id>spring-milestones</id>
+					<name>Spring Milestones</name>
+					<url>https://repo.spring.io/milestone</url>
+				</pluginRepository>
 			</pluginRepositories>
 		</profile>
 	</profiles>