Enable FF ci_trigger_forward_variables

What does this MR do and why?

This MR enables the FF ci_trigger_forward_variables by default.

The feature flag had stayed enabled for 2 weeks. Then, we disabled and made an improvement. Then, enabled again. Now, it's ready for enabled by default.

• Feature issue: #213729 (closed)
• Introduced in: !82676 (merged)
• Improved in: !84478 (merged)
• Rollout issue: #355572 (closed)

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