Fix repl discarding --build-depends (#8732)

* Fix repl discarding `build-depends` argument

Previously the function `\f -> L.allCondTrees $ traverseCondTreeC f` was
used to add the dependencies, but manipulating `CondTree` this way does
not update the nested fields `targetBuildDepends` of the tree, only the
conditions. It worked merely by chance if one does not further process
these fields: this explains why options like `--allow-newer` or
`allow-older` were incompatible with `--build-depends`.

Using `L.traverseBuildInfos . L.targetBuildDepends` ensures
`targetBuildDepends` fields and conditions are all updated consistently.

* Add test

* Add changelog

* Cleanup

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Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>