[JENKINS-38699] Only check for git repo in current workspace dir

The CliGit implementation of hasGitRepo() has the strange and surprising
behavior that if a workspace contains a directory named ".git" and that
directory is not a git repository (for example, an empty directory), then
command line git will search upwards in the file system tree to find a
git repository and will perform its operations on the repository it finds.

That is the right behavior for a user running command line git.  It allows
them to change to different directories and have the same experience
with command line git.

It is a dangerous behavior when deciding to run `git clean` or other
destructive operations in a Jenkins agent workspace.  If the agent
workspace is damaged, then the git commands search upwards, outside the
agent workspace.  This change causes the git plugin to only search in
the workspace, not any of the parent directories of the workspace.

Special thanks to @arpoch for patient work understanding the problem,
proposing a solution to the problem, and providing tests that show
the problem.

pom.xml

@@ -106,7 +106,7 @@
     <dependency>
       <groupId>org.jenkins-ci.plugins</groupId>
       <artifactId>git-client</artifactId>
-      <version>3.7.0</version>
+      <version>3.7.1-rc2780.420cdde29962</version>
     </dependency>
     <dependency>
       <groupId>org.jenkins-ci.plugins</groupId>

src/main/java/hudson/plugins/git/GitSCM.java

@@ -789,7 +789,7 @@ private PollingResult compareRemoteRevisionWithImpl(Job<?, ?> project, Launcher
 
         GitClient git = createClient(listener, environment, project, node, workingDirectory);
 
-        if (git.hasGitRepo()) {
+        if (git.hasGitRepo(false)) {
             // Repo is there - do a fetch
             listener.getLogger().println("Fetching changes from the remote Git repositories");
 
@@ -1205,7 +1205,7 @@ private void retrieveChanges(Run build, GitClient git, TaskListener listener) th
         List<RemoteConfig> repos = getParamExpandedRepos(build, listener);
         if (repos.isEmpty())    return; // defensive check even though this is an invalid configuration
 
-        if (git.hasGitRepo()) {
+        if (git.hasGitRepo(false)) {
             // It's an update
             if (repos.size() == 1)
                 log.println("Fetching changes from the remote Git repository");

src/main/java/jenkins/plugins/git/AbstractGitSCMSource.java

@@ -348,7 +348,7 @@ private <T, C extends GitSCMSourceContext<C, R>, R extends GitSCMSourceRequest>
             }
             GitClient client = git.getClient();
             client.addDefaultCredentials(getCredentials());
-            if (!client.hasGitRepo()) {
+            if (!client.hasGitRepo(false)) {
                 listener.getLogger().println("Creating git repository in " + cacheDir);
                 client.init();
             }

src/main/java/jenkins/plugins/git/GitSCMFileSystem.java

@@ -329,7 +329,7 @@ public SCMFileSystem build(@NonNull Item owner, @NonNull SCM scm, @CheckForNull
                     CredentialsProvider.track(owner, credential);
                 }
 
-                if (!client.hasGitRepo()) {
+                if (!client.hasGitRepo(false)) {
                     listener.getLogger().println("Creating git repository in " + cacheDir);
                     client.init();
                 }
@@ -391,7 +391,7 @@ public SCMFileSystem build(@NonNull SCMSource source, @NonNull SCMHead head, @Ch
                 }
                 GitClient client = git.getClient();
                 client.addDefaultCredentials(gitSCMSource.getCredentials());
-                if (!client.hasGitRepo()) {
+                if (!client.hasGitRepo(false)) {
                     listener.getLogger().println("Creating git repository in " + cacheDir);
                     client.init();
                 }

src/main/java/jenkins/plugins/git/GitToolChooser.java

@@ -102,7 +102,7 @@ private boolean decideAndUseCache(String remoteName) throws IOException, Interru
             if (cacheDir != null) {
                 Git git = Git.with(TaskListener.NULL, new EnvVars(EnvVars.masterEnvVars)).in(cacheDir).using("git");
                 GitClient client = git.getClient();
-                if (client.hasGitRepo()) {
+                if (client.hasGitRepo(false)) {
                     long clientRepoSize = FileUtils.sizeOfDirectory(cacheDir) / 1024; // Conversion from Bytes to Kilo Bytes
                     if (clientRepoSize > sizeOfRepo) {
                         if (sizeOfRepo > 0) {