Fix fusion file uploads where IFile is in a list

[Enterprize1]

Because discovering files in a ListValueNode called .Value on the items the CollectFiles method was called with the wrong type leading the discovery mechanism to not look inside the Nodes contained in a list.

Closes #7093

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.18%. Comparing base (9515881) to head (d4b394e).

Files	Patch %	Lines
...Abstractions/Serialization/Utf8JsonWriterHelper.cs	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7094      +/-   ##
==========================================
- Coverage   79.75%   79.18%   -0.58%     
==========================================
  Files        2645     2662      +17     
  Lines      132626   133189     +563     
==========================================
- Hits       105781   105468     -313     
- Misses      26845    27721     +876     

Flag	Coverage Δ
unittests	79.18% <0.00%> (-0.58%)	:arrow_down:

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[michaelstaib]

Thanks for contributing ... I will have a look at it.