PrestaShop nightly image unavailable

[jokesterfr]

Having an up-to-date nightly can be useful for at least:

• you can weekly run your tests on it, to detect any unexpected breaking changes with your module
• you can run daily E2E tests on the PrestaShop Core feature set

This suggest to rely on a webhook mechanism to trigger the prestashop-flashlight CI once a hook is emitted from the Core. Not sure how to make this happen, but any help is welcome.

The build.sh script should also be adapted to allow a build from the last nightly build available.