docs: Re-add missing cookie banner env var in build (#56889)

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A or Added/Fixed/Improved ...

.github/workflows/run_tests.yml

@@ -668,6 +668,7 @@ jobs:
     runs-on: namespace-profile-16x32-ubuntu-2204
     env:
       DOCS_AMPLITUDE_API_KEY: ${{ secrets.DOCS_AMPLITUDE_API_KEY }}
+      DOCS_CONSENT_IO_INSTANCE: ${{ secrets.DOCS_CONSENT_IO_INSTANCE }}
       CC: clang
       CXX: clang++
     steps: