Make the bdd tests exit code gating

[dannystaple]

In .github/workflows/on_call_staging_test.yaml, the "Run as service and test step" runs the bdd tests, and stores their failure in bdd_exit_code.

This currently only warns. However, since the tests pass now, we can close the gate and store this result in exit_code instead, along with showing an emoji red cross when they fail.

The message about "this is expected" should be removed. This should make the workflow simpler.

Acceptance criteria:

• Editorconfig convention followed
• The bdd_exit_code variable is removed in favour of using exit_code instead.
• The fail message has a red cross and no longer suggests that the failure is expected.
• The workflow still stops the service after all tests and exist with the exit code.
• The comment about don't fail on BDD tests for now is removed.