MassInstallAction: Install the Downgrade workflow on this repository

[Krastanov]

This pull request sets up the Downgrade workflow on this repository. cc: @Krastanov

[Krastanov]

The value of having this in CI is to ensure you are not inadvertently depending on features available only in recent versions of your dependencies. It also helps against accidentally having your users resolve to an antiquated version of dependencies (that is not really checked in CI). For more info, check this discussion: https://discourse.julialang.org/t/psa-add-downgrade-ci-to-better-check-version-compatibility/110063 (I will add a newer version of this action that solves some resolver issues, available since Julia con and already used in the SciML ecosystem)

It has already detected broken lower compat bounds in other repos in JuliaGraphs

It seems it also has found an inconsistent lower bound here -- GeometryBasics 0.4 does not export the various point types used in this package.

I believe this PR is ready for merging.