Upstreaming updates to theme to be compatible with Hugo v0.146.0 >= (#981)

### Prerequisites

Put an `x` into the box(es) that apply:

- [ ] This pull request fixes a bug.
- [ ] This pull request adds a feature.
- [x] This pull request introduces breaking change.

### Description

These changes are needed to not break the new Hugo build process based
on file changes introduced in Hugo v0.146.0.

### Issues Resolved

#977

### Checklist

Put an `x` into the box(es) that apply:

#### General

- [x] Describe what changes are being made
- [x] Explain why and how the changes were necessary and implemented
respectively
- [x] Reference issue with `#<ISSUE_NO>` if applicable

#### Resources

- [x] If you have changed any SCSS code, run `make release` to
regenerate all CSS files

#### Contributors

- [x] Add yourself to `CONTRIBUTORS.md` if you aren't on it already