chore: bump gitlab-zoekt chart to 3.9.0 on 9-9-stable

What does this MR do?

Bumps the gitlab-zoekt chart dependency from 3.8.1 to 3.9.0 in Chart.yaml and Chart.lock.

This is step 5 of the backport chain for 18.9 (SM).

Backport chain for 18.9 (SM)

1. ✅ gitlab-zoekt-indexer — tagged v1.8.2 on 18-9-stable
2. ✅ gitlab-org/build/CNG — gitlab-org/build/CNG!2896 (merged), builds cng/gitlab-zoekt:v1.8.2 on 18-9-stable
3. ✅ gitlab-org/gitlab — gitlab-org/gitlab!231352 (merged) bumping GITLAB_ZOEKT_VERSION to 1.8.2
4. ✅ cloud-native/charts/gitlab-zoekt — gitlab-org/cloud-native/charts/gitlab-zoekt!152 (merged), chart 3.9.0 with image v1.8.2 on 18-9-stable
5. ⭐ gitlab-org/charts/gitlab — this MR on 9-9-stable bumping gitlab-zoekt to 3.9.0

Related issues

• Original issue: gitlab-org/gitlab#593947 (closed)
• Original MR: gitlab-org/gitlab-zoekt-indexer!852 (merged)

Author checklist

For general guidance, please follow our Contributing guide.

Required

For anything in this list which will not be completed, please provide a reason in the MR discussion.

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated. ❌ nothing to update
• Tests added/updated, and test plan for scenarios not covered by automated tests. ❌ nothing to update
• Equivalent MR/issue for omnibus-gitlab opened. ❌ zoekt not deployed as part of omnibus

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab chart.