fix: add update server to default csp rules

[kulmann]

Description

While testing https://github.com/opencloud-eu/opencloud/pull/1617 I found out that we forgot to add the update server to the default csp rules.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Technical debt
• [ ] Tests only (no source changes)