fix!: Fix group amino codec (backport #13307)

[mergify]

This is an automatic backport of pull request #13307 done by Mergify.
Cherry-pick of 340c01b has failed:

On branch mergify/bp/release/v0.46.x/pr-13307
Your branch is up to date with 'origin/release/v0.46.x'.

You are currently cherry-picking commit 340c01bf5.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   x/group/codec/cdc.go
	new file:   x/group/codec/doc.go
	modified:   x/group/msgs.go
	modified:   x/group/msgs_test.go

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   CHANGELOG.md
	both modified:   docs/core/encoding.md
	both modified:   x/auth/types/codec.go
	both modified:   x/auth/vesting/types/codec.go
	both modified:   x/authz/codec.go
	both modified:   x/bank/types/codec.go
	both modified:   x/crisis/types/codec.go
	both modified:   x/distribution/types/codec.go
	both modified:   x/evidence/types/codec.go
	both modified:   x/feegrant/codec.go
	deleted by us:   x/gov/codec/doc.go
	both modified:   x/gov/types/v1/codec.go
	both modified:   x/gov/types/v1beta1/codec.go
	both modified:   x/group/codec.go
	both modified:   x/group/simulation/operations_test.go
	both modified:   x/mint/types/codec.go
	both modified:   x/slashing/types/codec.go
	both modified:   x/staking/types/codec.go
	both modified:   x/upgrade/types/codec.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[julienrbrt]

No backport. Fixed in 0.47.