Test JGit servlet-4 against Gerrit stable-3.13

The servlet-4 work in JGit now targets Gerrit 3.13 rather than 3.12.
Update the Jenkins shared pipeline so validation runs against the new
stable branch, keeping CI aligned with the intended integration target.

This ensures the servlet-4 branch is continuously built and tested with
Gerrit 3.13 (and master), catching incompatibilities earlier and keeping
the validation matrix current with the upcoming release [1].

[1] https://www.gerritcodereview.com/2025-09-17-gerrit-3.13-release-plan.html

Change-Id: I7bcd8e0624f5952409faa54963f790647f9613de

Author: syntonyze

vars/gerritJGitServlet4Pipeline.groovy

@@ -15,7 +15,7 @@
 // limitations under the License.
 
 /**
- * Declarative pipeline for building and testing JGit servlet-4 branch against Gerrit stable-3.12 and Gerrit master.
+ * Declarative pipeline for building and testing JGit servlet-4 branch against Gerrit stable-3.13 and Gerrit master.
  *  Parameters: None
  * Usage in a Jenkinsfile:
  *   gerritJGitServlet4Pipeline()
@@ -64,15 +64,15 @@ def call(Map cfg = [:]) {
         }
       }
 
-      stage('Checkout Gerrit stable-3.12') {
+      stage('Checkout Gerrit stable-3.13') {
         steps {
           sh '''
-            git clone -b stable-3.12 --recursive https://gerrit.googlesource.com/gerrit
+            git clone -b stable-3.13 --recursive https://gerrit.googlesource.com/gerrit
           '''
         }
       }
 
-      stage('Build Gerrit stable-3.12') {
+      stage('Build Gerrit stable-3.13') {
         steps {
           script {
             def jgitSourceDir = "${env.WORKSPACE}/jgit"
@@ -81,7 +81,7 @@ def call(Map cfg = [:]) {
 
             sh """
                 echo "${jgitSourceDir} -> ${jgitTargetDir}"
-                mv ${jgitTargetDir} /tmp/jgit-3.12
+                mv ${jgitTargetDir} /tmp/jgit-3.13
                 ln -sfn ${jgitSourceDir} ${jgitTargetDir}
             """
 
@@ -94,12 +94,12 @@ def call(Map cfg = [:]) {
           }
         }
       }
-      stage('Test Gerrit stable-3.12') {
+      stage('Test Gerrit stable-3.13') {
         steps {
           dir('gerrit') {
             sh '''
               . set-java.sh 21
-              echo "running gerrit stable-3.12 tests..."
+              echo "running gerrit stable-3.13 tests..."
               bazelisk test \
                 --test_tag_filters=-flaky \
                 --flaky_test_attempts 3 \