fix: checkstyle error

Author: wanling0000

jablib/src/main/java/org/jabref/logic/git/GitHandler.java

@@ -8,7 +8,6 @@
 import java.nio.file.Path;
 import java.util.Optional;
 import java.util.Set;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.jabref.logic.JabRefException;
 import org.jabref.logic.git.prefs.GitPreferences;
@@ -25,7 +24,6 @@
 import org.eclipse.jgit.lib.RepositoryState;
 import org.eclipse.jgit.lib.StoredConfig;
 import org.eclipse.jgit.merge.MergeStrategy;
-import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.transport.CredentialsProvider;
 import org.eclipse.jgit.transport.RefSpec;
 import org.eclipse.jgit.transport.URIish;