Fixing Build status for step bundles

[lpusok]

Checklist

• I've read and followed the Contribution Guidelines
• README.md is updated with the changes (if needed)

Version

Requires a PATCH version update

Context

BITRISE_BUILD_STATUS env was not set to failing inside a Step bundle.

workflows:
  debug:
    steps:
    - bundle::failing_step_bundle: { }

step_bundles:
  failing_step_bundle:
    title: Failing step
    steps:
    - script@1:
        title: Failing step
        inputs:
        - content: |-
            #!/usr/bin/env bash
            set -ex
            exit 1
    - script@1:
        title: Build status NOT failing
        is_always_run: true
        inputs:
        - content: |-
            #!/usr/bin/env bash
            set -ex
            # Ouptuts "0", incorrectly
            echo "$BITRISE_BUILD_STATUS"

Changes

Investigation details

Decisions

[godrei]

Do we need this log in long term?

[godrei]

Can we also add a test case for verifying the failed step env vars within a step bundle?