Fix state leakage in AbstractAsyncThreadContextTestBase (#3945)

Author: Kcruz28

log4j-core-test/src/test/java/org/apache/logging/log4j/core/async/AbstractAsyncThreadContextTestBase.java

@@ -48,6 +48,7 @@
 import org.apache.logging.log4j.util.ProviderUtil;
 import org.apache.logging.log4j.util.Unbox;
 import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.parallel.ResourceLock;
 
 @UsingStatusListener
@@ -59,6 +60,11 @@ public abstract class AbstractAsyncThreadContextTestBase {
 
     private static TestProperties props;
 
+    @BeforeEach
+    public void beforeEach() {
+        ThreadContext.clearAll();
+    }
+
     @BeforeAll
     public static void beforeClass() {
         props.setProperty("log4j2.enableThreadlocals", true);