[PP-1] Remove `system.theme` entry from \Drupal\Core\Config\Schema\SchemaCheckTrait::$ignoredPropertyPaths

The issue summary describes the problem, but the title does not.

Adding related issue.

@narendraR Thanks, that's a better title!

This issue will need to add a test that explicitly proves that the system module can be installed without triggering a validation error … ah, that's why we need 📌 Add validation constraints to system.theme Needs work to land first! 😄

I proposed a solution — thoughts?

What is this issue postponed on? Whatever it is, it should be list in the remaining tasks, according to the description of that field → , and the status changed.

Wouldn't 📌 Add validation constraints to system.theme Needs work need to make the default theme nullable for this to work?

@quietone made the order a bit more explicit, although I'm not sure these can be tackled separately.

#7: Yes, it would. And along with that, it'd need a validation constraint that treats null as invalid if >=1 theme is installed.

Correct status and added to "remaining tasks" as per #6