docker http build should use the tag of the pipeline run, not the latest tag

In https://community-tc.services.mozilla.com/tasks/B2oxyx2wSbmYzouCZLw18Q/runs/1/logs/public/logs/live.log, the task was run with v0.0.596. While the pipeline was running, we released v0.0.598.

The task should have downloaded models corresponding to the v0.0.596 pipeline run, but instead it tried to retrieve v0.0.598 models and failed because there was no run corresponding with v0.0.598.

It was actually a good failure, because if we had done a run with v0.0.598, then this task would have picked up a model from v0.0.598 while it was running v0.0.596 code.

We should make sure the task picks up the right version.

live_backing.log

This is likely because we are setting BUGBUG_VERSION to the right version (https://github.com/mozilla/bugbug/blob/59f1d1a69b0b1ce19941403123992075fe7d796d/infra/data-pipeline.yml#L1473), but then we are not setting TAG (https://github.com/mozilla/bugbug/blob/59f1d1a69b0b1ce19941403123992075fe7d796d/http_service/Dockerfile.bg_worker#L21), and we use TAG to choose the model version to download (https://github.com/mozilla/bugbug/blob/59f1d1a69b0b1ce19941403123992075fe7d796d/bugbug/utils.py#L267).