Update Mocking of TestContext

Recent Spring Framework changes to default to Mockito's STRICT stubbing mode
requires that TestContext be mocked after the exection context has been fully
instantiated

Closes gh-15579

test/src/test/java/org/springframework/security/test/context/support/WithSecurityContextTestExecutionListenerTests.java

@@ -20,11 +20,11 @@ import java.lang.reflect.Method;
 import java.util.function.Supplier;
 
 import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.ArgumentCaptor;
 import org.mockito.ArgumentMatchers;
-import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 
 import org.springframework.beans.factory.annotation.Autowired;
@@ -42,6 +42,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 
@@ -56,11 +57,15 @@ public class WithSecurityContextTestExecutionListenerTests {
 	@Autowired
 	private ApplicationContext applicationContext;
 
-	@Mock
 	private TestContext testContext;
 
 	private WithSecurityContextTestExecutionListener listener = new WithSecurityContextTestExecutionListener();
 
+	@BeforeEach
+	public void setup() {
+		this.testContext = mock(TestContext.class);
+	}
+
 	@AfterEach
 	public void cleanup() {
 		TestSecurityContextHolder.clearContext();