### Description of the change
In the act_runner StatefulSet, this allows to mount volumes.
### Benefits
It allows to mount some volumes in any of the two containers, e.g. certificates for a private registry.
### Possible drawbacks
I can't think of any.
### Applicable issues
- Fixes#744
### Checklist
- [X] Parameters are documented in the `values.yaml` and added to the `README.md` using [readme-generator-for-helm](https://github.com/bitnami-labs/readme-generator-for-helm)
- [X] Helm templating unittests are added (required when changing anything in `templates` folder)
Co-authored-by: Xav <grandmou@protonmail.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/756
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.com>
Co-authored-by: grandmou <grandmou@noreply.gitea.com>
Co-committed-by: grandmou <grandmou@noreply.gitea.com>