Watch 5.3.x branch in the CI pipeline

Main branch has moved to the 6.0.x line, so this commit updates this CI
pipeline to the new 5.3.x maintenance branch.

ci/parameters.yml

@@ -5,7 +5,7 @@ github-repo: "https://github.com/spring-projects/spring-framework.git"
 github-repo-name: "spring-projects/spring-framework"
 docker-hub-organization: "springci"
 artifactory-server: "https://repo.spring.io"
-branch: "main"
+branch: "5.3.x"
 milestone: "5.3.x"
 build-name: "spring-framework"
 pipeline-name: "spring-framework"