Add CI tests to ensure created backups are valid

Thanks for the follow-up @solideogloria!

I think, it might make sense to implement validatons on the resulting backup file generation in this module (I think this is not a test running on the actual backups taken on Drupal sites). I guess that would be a different and probably hard to implement feature.

As first step a helper class could be implemented for such tests, for example to check the validity based on general metrics or static validations? I'm not aware, which techniques are best to check these backups. Maybe one could look into similar open source tools? Maybe the database engines offer some tools or something like that.

Maybe most simple tests bring the most quick and largest WIN, like to example checking the backups contain valid SQL (and nothing else like trailing HTML or error message like reported in the previous issue).
This issue can become extremely complex, but starting simple might be better.

I think that, for starters, it would be easiest to import a SQL file, create a backup, then check that the backup file is the same as the imported file? Then do the same with gzip enabled.

This should not be a feature for users of the module, but CI tests for this module to create working backups as expected.
Everything else should be a separate issue, please. As written above, I'm unsure, how hard it will be to test created backups automatically in user environments.

Clarified the title and description.

Thank you for creating this issue.

Test coverage to confirm the backup works is 100% the way to go.