Fix stuck bridge jobs when downstream project is invalid

What does this MR do?

This MR fixes stuck bridge jobs when the downstream project is invalid.

We normally try to handle this in Ci::CreateDownstreamPipelineService but the code doesn't reach there since we make the bridge job stuck in the "pending" state.

In this MR, we don't check the existence of the project in the model. We pass this logic into the worker that already does.

Related to #331703 (closed)

Note: We also have the same problem for "mirroring the status from an upstream pipeline", however, I'll create another MR for that.

Screenshots or Screencasts (strongly suggested)

test:
  script: exit 0

deploy:
  trigger:
    project: my/invalid-project

Before:

After:

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