When using the Bubble Skin of the Testimonial Carousel widget and with the image aligned to the left or right, the content will be aligned to the top of the container. This may not be an issue if the image is at the default size. However, once the image size is increased, this condition becomes more apparent.
Thanks to Helmut H. Göbel for asking the question on the Elementor Facebook Group.
The following CSS will center the content in the Testimonial Carousel container.