tests/aio: Clean up global variable shadowing

Rename the argument to fix:

  tests/unit/test-aio.c:130:44: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
  static void set_event_notifier(AioContext *ctx, EventNotifier *notifier,
                                             ^
  tests/unit/test-aio.c:22:20: note: previous declaration is here
  static AioContext *ctx;
                     ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20231009100251.56019-9-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/unit/test-aio.c

@@ -127,10 +127,10 @@ static void *test_acquire_thread(void *opaque)
     return NULL;
 }
 
-static void set_event_notifier(AioContext *ctx, EventNotifier *notifier,
+static void set_event_notifier(AioContext *nctx, EventNotifier *notifier,
                                EventNotifierHandler *handler)
 {
-    aio_set_event_notifier(ctx, notifier, handler, NULL, NULL);
+    aio_set_event_notifier(nctx, notifier, handler, NULL, NULL);
 }
 
 static void dummy_notifier_read(EventNotifier *n)