fix: nested iterator on cache store (backport #14798)

[mergify]

This is an automatic backport of pull request #14798 done by Mergify.
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Changes to be committed:
	modified:   store/cachekv/internal/btree.go
	modified:   store/cachekv/store.go
	modified:   store/cachekv/store_test.go

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	both modified:   CHANGELOG.md

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[julienrbrt]

utACK. As said here #14798 (review) this will need to be tested on mainnets again.

[tac0turtle]

We can merge so we can pull the release branch.