Update a reference to the build pipeline

Author: sdeleuze

ci/README.adoc

@@ -2,7 +2,7 @@
 
 The Spring Framework uses https://concourse-ci.org/[Concourse] for its CI build and other automated tasks.
 The Spring team has a dedicated Concourse instance available at https://ci.spring.io with a build pipeline
-for https://ci.spring.io/teams/spring-framework/pipelines/spring-framework-6.0.x[Spring Framework 6.0.x].
+for https://ci.spring.io/teams/spring-framework/pipelines/spring-framework-6.1.x[Spring Framework 6.1.x].
 
 === Setting up your development environment