Automate bumping the helm-chart version

[jsjoeio]

We automate bumping a lot of stuff as part of the release-prep.sh script. One thing that isn't automated though is bumping the helm-chart version.

Example where we do this: https://github.com/coder/code-server/pull/4273/files

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no activity occurs in the next 5 days.