esp_ringbuf: don't test xRingbufferCreate with cache disabled

Creating a ringbuffer is not an operation that needs to be done when
the cache is disabled.

components/esp_ringbuf/test/test_ringbuf.c

@@ -673,8 +673,8 @@ static IRAM_ATTR __attribute__((noinline)) bool iram_ringbuf_test()
 {
     bool result = true;
 
-    spi_flash_guard_get()->start(); // Disables flash cache
     RingbufHandle_t handle = xRingbufferCreate(CONT_DATA_TEST_BUFF_LEN, RINGBUF_TYPE_NOSPLIT);
+    spi_flash_guard_get()->start(); // Disables flash cache
     result = result && (handle != NULL);
     xRingbufferGetMaxItemSize(handle);
     vRingbufferDelete(handle);