MAINT: CI workflow for checking generate_aggregations

[VeckoTheGecko]

Is your feature request related to a problem?

I realised while reviewing #11471 that the aggregations on main are simply out of date!

Following the instructions in generate_aggregations.py updates the docstrings in meaningful ways.

I think it would be good to integrate a check in CI for this. Now that we're using Pixi that will be quite easy to maintain and also will help the local dev workflow.

Describe the solution you'd like

• A task pixi run generate-aggregations that generates the aggregations (easing local development).
• A github workflow (generate-aggregations-ci) that
  • generate-aggregations
  • runs pre-commit on top (coercing things accordingly)
  • checks if there is a dirty git tree (i.e., the committed files don't match). If so, the worflow will fail with an error message. If not, it will pass.

The workflow won't push the needed edits back to the PR since that sounds complicated with lots of edges.

Describe alternatives you've considered

Additional context

No response