fix: assert previous channel identifer is empty in Msg ValidateBasic (backport #1792)

[mergify]

This is an automatic backport of pull request #1792 done by Mergify.
Cherry-pick of 4a781e5 has failed:

On branch mergify/bp/release/v4.0.x/pr-1792
Your branch is up to date with 'origin/release/v4.0.x'.

You are currently cherry-picking commit 4a781e5.
  (fix conflicts and run "git cherry-pick --continue")
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Changes to be committed:
	modified:   docs/migrations/v3-to-v4.md
	modified:   modules/apps/27-interchain-accounts/controller/ibc_middleware_test.go
	modified:   modules/core/04-channel/types/msgs.go
	modified:   modules/core/04-channel/types/msgs_test.go
	modified:   testing/endpoint.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

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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