groot: add handling of top-level key with string payload

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 67.25%. Comparing base (ac11738) to head (9004c7e).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1009 +/- ## ========================================== + Coverage 67.23% 67.25% +0.02% ========================================== Files 491 492 +1 Lines 71877 71909 +32 ========================================== + Hits 48328 48365 +37 + Misses 21221 21213 -8 - Partials 2328 2331 +3 ```

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