As a commenter said, the spinner is appropriate while the system is processing the request or working to delete the list, because the user expects feedback after taking an action.
The issue with placing it in the bottom right side of the dialog window is that 1) it’s not a common place for a user to look to receive feedback, and 2) the buttons are presumably still both active (the user might want to click on them to try to cancel the action.)
Consider changing the buttons to “Delete” and “Cancel” to make it really clear to the user what they’re going to do. “Cancel” should close the window (the user really should never see a spinner). When “Delete” is clicked, both buttons should become disabled; a spinner is OK if the deletion only lasts a couple of seconds (for longer deletions, use a progress bar). Position the spinner either in the middle of the screen, or on the “Delete” button itself.