Do not import changes refs from GitHub

Importing changes refs may result in unexpected behaviour (especially
when they come from different Gerrit server) therefore they should be
excluded from the clone.

Bug: Issue 40014491
Change-Id: Iaec0505b67b19a0c04fcbda7a1785af50fc7c5fb

github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitCloneStep.java

diff --git a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitCloneStep.java b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitCloneStep.java
index 25d953b..69d1eac 100644
--- a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitCloneStep.java
+++ b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitCloneStep.java
@@ -109,7 +109,8 @@
     createNewProject();
     String sourceUri = getSourceUri();
     try (Git git = Git.open(destinationDirectory)) {
-      FetchCommand fetch = git.fetch().setRefSpecs("refs/*:refs/*").setRemote(sourceUri);
+      FetchCommand fetch =
+          git.fetch().setRefSpecs("^refs/changes/*", "refs/*:refs/*").setRemote(sourceUri);
       fetch.setCredentialsProvider(getRepository().getCredentialsProvider());
       if (progress != null) {
         fetch.setProgressMonitor(progress);