fix(iam_user): use default organization id when available

[Codelax]

No description provided.

[codecov-commenter]

Codecov Report

Merging #1385 (d6e87f1) into master (b9b8015) will decrease coverage by 0.05%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1385      +/-   ##
==========================================
- Coverage   66.38%   66.33%   -0.06%     
==========================================
  Files         123      123              
  Lines       19624    19635      +11     
==========================================
- Hits        13027    13024       -3     
- Misses       5460     5473      +13     
- Partials     1137     1138       +1     

Impacted Files	Coverage Δ
scaleway/data_source_iam_user.go	0.00% <0.00%> (ø)
scaleway/helpers_iam.go	0.00% <0.00%> (ø)
scaleway/retryable_transport.go	70.00% <0.00%> (-10.00%)	⬇️

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