Unable to use Buildkite `trigger`

[alabeduarte]

Hi there 👋

First of all, thank you for this plugin, I have been looking for something similar for some time and it seems I just found it!

There is an issue I'd like to check with you is that I'm currently unable to use Buildkite trigger as it errors out due to the following:

`env` is not a valid property on the `trigger` step. Please check the documentation to get a full list of supported properties.

This seems similar to the issue #39 but what it seems to be the case with me is that even though I don't specify global any env, it tries to add to buildpipe generated yaml anyway.

Here's an example:

Given the dynamic pipeline below:

env:
  FOO: bar

projects:
  - label: "my-project"
    path:
      - internal/foo
    key: deploy
    trigger: "another-pipeline"
    build:
      env:
        BUILDPIPE_SCOPE: project

The result I get is the following:

  | [2022-12-20T04:44:49Z]   build:
  | [2022-12-20T04:44:49Z]     env:
  | [2022-12-20T04:44:49Z]       BUILDPIPE_SCOPE: project
  | [2022-12-20T04:44:49Z]   env:
  | [2022-12-20T04:44:49Z]     FOO: bar
  | [2022-12-20T04:44:49Z]   key: deploy
  | [2022-12-20T04:44:49Z]   label: 'my-project'
  | [2022-12-20T04:44:49Z]   trigger: another-pipeline

As you can see above, buildpipe is adding the key env to the same level as build, which is not supported.

Even if I remove the global environment variables, I get the same error as the env is still being added:

# no global env vars this time
projects:
  - label: "my-project"
    path:
      - internal/foo
    key: deploy
    trigger: "another-pipeline"
    build:
      env:
        BUILDPIPE_SCOPE: project

Output:

  | [2022-12-20T04:44:49Z]   build:
  | [2022-12-20T04:44:49Z]     env:
  | [2022-12-20T04:44:49Z]       BUILDPIPE_SCOPE: project
  | [2022-12-20T04:44:49Z]   env: {}
  | [2022-12-20T04:44:49Z]   key: deploy
  | [2022-12-20T04:44:49Z]   label: 'my-project'
  | [2022-12-20T04:44:49Z]   trigger: another-pipeline

As you can see above, the key env is being generated but it is empty (i.e. env: {}).

---

Let me know if this seems to be a legit issue or if I'm using the plugin wrong. Nevertheless, thank you for your work!

Cheers 🙏

[alabeduarte]

I just realised there is an open PR: #84