Fix TaxonomyLoadTree::resolve return typehint

[Kingdutch]

Fixes #952

[codecov]

Codecov Report

Merging #953 into 8.x-4.x will not change coverage.
The diff coverage is 0%.

@@            Coverage Diff             @@
##             8.x-4.x     #953   +/-   ##
==========================================
  Coverage      61.81%   61.81%           
- Complexity       678      679    +1     
==========================================
  Files             95       95           
  Lines           1409     1409           
==========================================
  Hits             871      871           
  Misses           538      538

Impacted Files	Coverage Δ	Complexity Δ
...GraphQL/DataProducer/Taxonomy/TaxonomyLoadTree.php	0% <0%> (ø)	24 <16> (+1)	⬆️

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