ci: fix invalid cfs-npm Dependabot registry configuration

[ReubenBond]

Dependabot cannot parse .github/dependabot.yml because the cfs-npm registry entry does not match a supported registry schema.

Observed on PR #10849 in check run https://github.com/dotnet/orleans/runs/100725909036:

The property '#/registries/cfs-npm/' of type object did not match one or more of the required schemas

Update the registry configuration to conform to the current Dependabot specification, then confirm the Dependabot configuration check succeeds.