Update exception variable names

Consistently use `ex` for caught exception and `cause` for Exception
constructor arguments.

Issue gh-8945

remoting/src/test/java/org/springframework/security/remoting/rmi/ContextPropagatingRemoteInvocationTests.java

@@ -69,7 +69,7 @@ public class ContextPropagatingRemoteInvocationTests {
 			remoteInvocation.invoke(TargetObject.class.newInstance());
 			fail("Expected IllegalArgumentException");
 		}
-		catch (IllegalArgumentException e) {
+		catch (IllegalArgumentException ex) {
 			// expected
 		}