Bump zoekt version to 0.8.1

What does this MR do?

This MR bumps the Zoekt image version to v0.8.1

Changes: https://gitlab.com/gitlab-org/gitlab-zoekt-indexer/-/compare/81565ece8d9deec88595314c872cf267c802d18b...4ad6c580a584e8993493cfc60e07e0bfb53c9802?from_project_id=46649240&straight=false

Related issues

Checklist

See Definition of done.

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

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated
• New dependencies are managed with dependencies.io