gomod: bump zoekt
Created by: keegancsmith
includes
- https://github.com/sourcegraph/zoekt/commit/629b7ab indexserver: remove feature flag for explode
- https://github.com/sourcegraph/zoekt/commit/dbb88ea indexserver: add IndexConcurrency for concurrent index jobs
- https://github.com/sourcegraph/zoekt/commit/f331ab3 indexserver: introduce indexMutex
- https://github.com/sourcegraph/zoekt/commit/b5426a7 read: inline delta-varint decoding in unmarshalDocumentSections
Test Plan: ci