Fix: avoid unintended @@skip_touch_context persistence when @skip_touch_context is true

[knaito-asial]

Previously, touch_context used the expression:

return if @@skip_touch_context ||= false || @skip_touch_context ||= false

This unintentionally mutated @@skip_touch_context to true when @skip_touch_context was true and @@skip_touch_context was nil.
As a result, the class variable remained true across subsequent requests, even though the instance variable was correctly reset.
This led to touch_context being skipped globally, even in contexts where it should have run.

To fix this, we now evaluate both flags independently to avoid side-effects:

skip1 = defined?(@@skip_touch_context) ? @@skip_touch_context : false
skip2 = @skip_touch_context.nil? ? false : @skip_touch_context
return if skip1 || skip2

Example of the bug in production

• When a user reorders modules via the course UI (e.g. moving a module up or down), the controller saves the modules using save_without_touching_context, which sets @skip_touch_context = true.
• Because of the above bug, @@skip_touch_context is unintentionally set to true and never reset.
• Then, when the user creates a new announcement, the touch_context on the DiscussionTopic model is skipped.
• As a result, the course's updated_at is not updated, and the announcement is not shown to students due to stale cache.

Let me know if any additional context is helpful!