Create jest and testing-library dependabot group

[bmuenzenmeyer]

Now that Dependabot is working again, resolved via #5550 we should further refine our groupings.
I'd argue that all lint-related work should always change in lockstep.

Looking at the above, I'd propose a testing group:

• take the testing-library group
• add meta: bump jest and @types/jest #5555 to it