Repository: runatlantis/atlantis (language: go)

Issue:
post_workflow_hooks + env: cannot unmarshal !!map into string
### Overview of the Issue

When `env` is defined in `post_workflow_hooks`, Atlantis fails to start with the following message:

```
Error: initializing server: parsing /repos.yaml file: yaml: unmarshal errors:
  line 31: cannot unmarshal !!map into string
```

Removing the offending `env` definition fixes the issue.

### Reproduction Steps

repos.yaml snippet that causes the issue:

```
    post_workflow_hooks:
      - env:
          name: INFRACOST_SKIP_UPDATE_CHECK
          value: 1
```

### Environment details

Tested with Atlantis 0.19.4 and 0.19.5-pre.20220616

### Additional details

It seems Atlantis does not support anything other than `run` steps in workflow hooks (see https://github.com/runatlantis/atlantis/blob/master/server/core/config/raw/workflow_step.go#L14-L20).


Discussion / hints:

Fix patch:
diff --git a/runatlantis.io/docs/post-workflow-hooks.md b/runatlantis.io/docs/post-workflow-hooks.md
index 317eddd906..577b677541 100644
--- a/runatlantis.io/docs/post-workflow-hooks.md
+++ b/runatlantis.io/docs/post-workflow-hooks.md
@@ -6,6 +6,8 @@ workflows](custom-workflows.html#custom-run-command) in that they are run
 outside of Atlantis commands. Which means they do not surface their output
 back to the PR as a comment.
 
+Post workflow hooks also only allow `run` commands.
+
 [[toc]]
 
 ## Usage
diff --git a/runatlantis.io/docs/pre-workflow-hooks.md b/runatlantis.io/docs/pre-workflow-hooks.md
index a84f91e9c6..33dff00b3a 100644
--- a/runatlantis.io/docs/pre-workflow-hooks.md
+++ b/runatlantis.io/docs/pre-workflow-hooks.md
@@ -8,6 +8,7 @@ workflows](custom-workflows.html#custom-run-command) in several ways.
    present. This be utilized to [dynamically generate repo configs](pre-workflow-hooks.html#dynamic-repo-config-generation).
 2. Pre workflow hooks are run outside of Atlantis commands. Which means
    they do not surface their output back to the PR as a comment.
+3. Pre workflow hooks only allow `run` commands.
 
 [[toc]]
 


Test patch: