Make invalidations count visible in workflow run name

Since September 2022 one can apparently use dynamic names for workflow runs. Could/should we maybe use this to put the number of invalidations on `main` and on the currently tested `PR` in the workflow name, such that one does not have to look it up manually each time?

See [this blog post](https://github.blog/changelog/2022-09-26-github-actions-dynamic-names-for-workflow-runs/) or the [docs](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#name).

Sometimes we get an "increase by one invalidation" error which has often (always?) been a transient issue, so this makes it "safer" to ignore a failed invalidation workflow (and conversely, makes you take it more seriously if the number of invalidations increases significantly)

Inspect the GitHub Actions workflow definitions and the linked workflow-run naming documentation first. Identify the workflow that performs invalidation checks, then determine how the main and tested PR invalidation counts can be included in its run name; done means the counts are visible and update correctly for those runs.

Written by the indexing model from the issue text.