[9.x] Show error if key:generate artisan command fails

[mbardelmeijer]

This PR changes that if the artisan key:generate fails, an error message is shown.

This is most common when the .env file is missing an APP_KEY= empty placeholder. In this case, the preg_replace call will return the input as-is. If that happened, an error is shown instead of showing the incorrect Application key set successfully.

Fixes #44917

[driesvints]

Good one 👍

[LukeTowers]

@driesvints @mbardelmeijer is there any interest in using something like the Laravel Config Writer provided by @wintercms (see https://github.com/wintercms/laravel-config-writer/blob/main/README.md#environment-files) to more reliably handle these issues rather than just failing?

[driesvints]

@LukeTowers appreciate it but I don't think so no.