[JENKINS-73781] Replace JGit peel() with getRefDatabase().peel()

https://issues.jenkins.io/browse/JENKINS-73781 notes that JGit
deprecated peel() in favor of getRefDatabase().peel() a long time ago.
The deprecated method was removed from JGit 7.0.0.  This uses the
replacement method that has been available since the deprecation.

jenkinsci/git-client-plugin#1170 is the git
client plugin pull request that introduced JGit 7.0.0.

https://github.com/jenkinsci/git-client-plugin/releases/tag/git-client-6.0.0
is the git client plugin release that introduced JGit 7.0.0.

src/main/java/com/github/jenkins/lastchanges/impl/GitLastChanges.java

@@ -216,7 +216,7 @@ public int compare(Ref o1, Ref o2) {
 
             if (tags != null && !tags.isEmpty()) {
                 Ref tag = tags.get(0);
-                Ref peeledRef = repository.peel(tag);
+                Ref peeledRef = repository.getRefDatabase().peel(tag);
                 LogCommand log = git.log();
                 if (peeledRef.getPeeledObjectId() != null) {
                     log.add(peeledRef.getPeeledObjectId());