Badger v4.9.0 Released

[matthewmcneely]

We're pleased to announce the release of badger v4.9.0. See https://github.com/dgraph-io/badger/releases/tag/v4.9.0.

Note: for users of badger's y utility package, a change was made to SafeCopy so that it never returns a null reference. See that PR for more information.