update CI scripts

[isaacsas]

It would be nice to separate out extension testing from the primary CI. This would help test Catalyst core against the latest versions of packages, which a user would likely install when adding it, and which can be needed for us to work as a downstream test for MTK. Separate tests should then be setup for extensions (which might pull older versions of some core dependencies due to compat issues in the weakdeps). I'm not sure how to configure this, but it would be nice to have.

Along those lines, we should setup to use the SciML reusable-CI script, with any custom modifications we may need (for example, disabling failures from dep warnings on dependencies we don't control -- the never ending stream of such failures is why we haven't yet managed to merge the updated CI script PR...).

[isaacsas]

Closed by #1094