fix: working hash with initial version (backport #943)

[mergify]

Context

InitialVersion is not reflected in the WorkingHash calculation, only reflected in the SaveVersion. This will lead to the AppHash mismatch while upgrading, since the the hash of the root is already calculated in the WorkingHash and won't re-calculated in the SaveVersion which is wrong.

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This is an automatic backport of pull request #943 done by Mergify.

[mergify]

Cherry-pick of 70f77c2 has failed:

On branch mergify/bp/master/pr-943
Your branch is up to date with 'origin/master'.

You are currently cherry-picking commit 70f77c2.
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Changes to be committed:
	modified:   mutable_tree.go
	modified:   tree_test.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/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally