Prepare 3.1.x branch

buildSrc/src/main/java/org/springframework/boot/build/AsciidoctorConventions.java

@@ -134,7 +134,7 @@ class AsciidoctorConventions {
 
 	private String determineGitHubTag(Project project) {
 		String version = "v" + project.getVersion();
-		return (version.endsWith("-SNAPSHOT")) ? "main" : version;
+		return (version.endsWith("-SNAPSHOT")) ? "3.1.x" : version;
 	}
 
 	private void configureOptions(AbstractAsciidoctorTask asciidoctorTask) {

ci/parameters.yml

@@ -3,7 +3,7 @@ github-repo-name: "spring-projects/spring-boot"
 homebrew-tap-repo: "https://github.com/spring-io/homebrew-tap.git"
 docker-hub-organization: "springci"
 artifactory-server: "https://repo.spring.io"
-branch: "main"
+branch: "3.1.x"
 milestone: "3.1.x"
 build-name: "spring-boot"
 concourse-url: "https://ci.spring.io"