Adapt remote branch listing test to CLI git 2.48.0 (#1242)

* Adapt GitAPITest for CLI git 2.48.0

Fetch from CLI git 2.48.0 and later return origin/HEAD

https://github.blog/open-source/git/highlights-from-git-2-48/ says:

> With Git 2.48, if the remote has a default branch but refs/remotes/origin/HEAD
> is missing locally, then a fetch will update it.

This test was unintentionally testing the behavior of CLI git before
2.48.0.  Other tests in GitClientFetchTest were testing that origin/HEAD
was reported as a branch.

* Show names/sha1 of detected branches on failure

When the assertion fails, show the details of the set of branches so
that the test failure has more information about the failure conditions.

Thanks to @darinpope for the question that prompted the improvement

* Remove unused cliGitCommand from GitAPITest

Author: MarkEWaite

src/test/java/org/jenkinsci/plugins/gitclient/GitAPITest.java

@@ -87,7 +87,6 @@ public class GitAPITest {
 
     private GitClient testGitClient;
     private File testGitDir;
-    private CliGitCommand cliGitCommand;
 
     public GitAPITest(final String gitImplName) {
         this.gitImplName = gitImplName;
@@ -167,7 +166,6 @@ public void setUpRepositories() throws Exception {
 
         testGitClient = workspace.getGitClient();
         testGitDir = workspace.getGitFileDir();
-        cliGitCommand = workspace.getCliGitCommand();
         workspace.initializeWorkspace();
     }
 
@@ -760,7 +758,26 @@ public void testListRemoteBranches() throws Exception {
         workspace.launchCommand("git", "fetch", "origin");
         Set<Branch> branches = testGitClient.getRemoteBranches();
         assertBranchesExist(branches, "origin/" + defaultBranchName, "origin/test", "origin/another");
-        assertEquals(3, branches.size());
+        int branchCount = 3;
+        if (workspace.cgit().isAtLeastVersion(2, 48, 0, 0)) {
+            /* Fetch from CLI git 2.48.0 and later return origin/HEAD
+             *
+             * https://github.blog/open-source/git/highlights-from-git-2-48/ says:
+             *
+             * With Git 2.48, if the remote has a default branch but refs/remotes/origin/HEAD
+             * is missing locally, then a fetch will update it.
+             *
+             * This test was unintentionally testing the behavior of CLI git before
+             * 2.48.0.  Other tests in GitClientFetchTest were testing that origin/HEAD
+             * was reported as a branch.
+             */
+            assertBranchesExist(branches, "origin/HEAD");
+            branchCount = 4;
+        }
+        assertEquals(
+                "Wrong branch count, found " + branches.size() + " branches: " + branches,
+                branchCount,
+                branches.size());
     }
 
     @Test