Migrate from JUnit 4 to JUnit 5

Also resolves failing CI workflow:

https:
//github.com/KorAP/Kustvakt/actions/runs/6261950074/job/17017180336

Change-Id: I31a71419f0443118e973112e0f621d52c11fd81e
diff --git a/full/src/test/java/de/ids_mannheim/korap/web/controller/VirtualCorpusTestBase.java b/full/src/test/java/de/ids_mannheim/korap/web/controller/VirtualCorpusTestBase.java
index 7b354b5..821a338 100644
--- a/full/src/test/java/de/ids_mannheim/korap/web/controller/VirtualCorpusTestBase.java
+++ b/full/src/test/java/de/ids_mannheim/korap/web/controller/VirtualCorpusTestBase.java
@@ -3,7 +3,7 @@
 import static org.hamcrest.CoreMatchers.hasItem;
 import static org.hamcrest.CoreMatchers.not;
 import static org.hamcrest.MatcherAssert.assertThat;
-import static org.junit.Assert.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import java.util.List;
 import java.util.Map.Entry;