[8.15] Fix screenshots for integrations upgrades (backport #1243)

[mergify]

This updates the outdated screenshots described in #1103

For the Nginx screencap, I've cropped it to just show the "New version available" warning, since it's very difficult to recreate (I'm not sure if it's possible to install an earlier version of an integration).

Closes: #1103

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This is an automatic backport of pull request #1243 done by [Mergify](https://mergify.com).

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