Mark LibraryOfCongressTest as a fetcher test (#3012)

Author: LinusDietz

src/test/java/org/jabref/logic/importer/fetcher/LibraryOfCongressTest.java

@@ -3,11 +3,14 @@
 import java.util.Optional;
 
 import org.jabref.model.entry.BibEntry;
+import org.jabref.testutils.category.FetcherTests;
 
 import org.junit.Test;
+import org.junit.experimental.categories.Category;
 
 import static org.junit.Assert.assertEquals;
 
+@Category(FetcherTests.class)
 public class LibraryOfCongressTest {
 
     private LibraryOfCongress fetcher = new LibraryOfCongress();