test: Fix potential flaky test cases in TracerTest (#1859)

sentinel-core/src/test/java/com/alibaba/csp/sentinel/TracerTest.java

@@ -17,12 +17,14 @@ public class TracerTest extends Tracer {
     public void setUp() {
         ContextTestUtil.cleanUpContext();
         ContextTestUtil.resetContextMap();
+        Tracer.exceptionPredicate = null;
     }
 
     @After
     public void tearDown() {
         ContextTestUtil.cleanUpContext();
         ContextTestUtil.resetContextMap();
+        Tracer.exceptionPredicate = null;
     }
 
     @Test