Merge branch 'process-commit-worker-migration-encoding' into 'master'

Encode when migrating ProcessCommitWorker jobs

## What does this MR do?

This adds encoding logic to the migration for ProcessCommitWorker, ensuring it doesn't throw errors when the input can not be converted to UTF-8 without extra help.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/25489

See merge request !8064