When loading nested modules, the child module diagnostics were dropped
in the recursive function. This mean that the config from the submodules
wasn't fully loaded, even though no errors were reported to the user.
This caused further problems if the plan was stored in a plan file, when
means only the partial configuration was stored for the subsequent apply
operation, which would result in unexplained "Resource node has no
configuration attached" errors later on.
Also due to the child module diagnostics being lost, any newly added
nested modules would be silently ignored until `init` was run again
manually.
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