conftest: Update to 0.34.0

Changes:
## 0.34.0
### New Features
- Add `parse_config` and `parse_config_file` Rego functions to allow unit
  testing using config file snippets. Find out how to use these at
  <https://www.conftest.dev/#writing-unit-tests>.

## 0.33.2
### Other improvements
- Bump OPA to v0.42.2

## 0.33.1
### Other improvements
- Bump OPA to v0.42.1

## 0.33.0
### Bug fixes
- Fix 404 error when using conftest push

### Other improvements
- Bump OPA to v0.42.0
- Bump Go to v1.18.3

(leot)