Disallow stopping build after upload step

Jiggle the button and show a warning.

Fixes #241

https://github.com/chromaui/addon-visual-tests/assets/321738/0f90eea4-2591-44d3-a3f5-c68e384283bd

📦 Published PR as canary version: 1.5.1--canary.317.42e6d13.0

:sparkles: Test out this PR locally via: ```bash npm install @chromatic-com/storybook@1.5.1--canary.317.42e6d13.0 # or yarn add @chromatic-com/storybook@1.5.1--canary.317.42e6d13.0 ```

chromaui / addon-visual-tests

Disallow stopping build after upload step #317