go.mod: Update Badger to v4.1.0
Badger has bumped its major version from v3 series to v4. This bump is mostly uninteresting, but there are two interesting changes in there:
- They have upgraded the minimum required Go version to 1.19. This
has kept us from upgrading Badger given that we still supported Go
1.18. This has changed with a17fb7823 (go.mod: Use Go 1.19 as
minimum required version, 2023-05-23) though, so we're unblocked
with the upgrade.
- They have changed their version schema from CalVer to SemVer,
meaning that future releases should be more indicative of real
major changes.
Other than that there are no real changes that would be interesting to us.
Closes #4890 (closed).