fix(docs): fix data transformation example

[pevers]

This PR fixes the data transformation example https://github.com/argoproj/argo-workflows/blob/master/examples/data-transformations.yaml by adding a target artifact.

Without this the workflow crashes with:

Error (exit code 64): unable to process data template: unable to process data source: unable to source artifact paths: template artifact location not set

Closes #6900 .

[codecov]

Codecov Report

Merging #6901 (1429a75) into master (2fd4b8a) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 1429a75 differs from pull request most recent head e4f8ad5. Consider uploading reports for the commit e4f8ad5 to get more accurate results

@@            Coverage Diff             @@
##           master    #6901      +/-   ##
==========================================
- Coverage   48.53%   48.53%   -0.01%     
==========================================
  Files         265      265              
  Lines       19259    19259              
==========================================
- Hits         9348     9347       -1     
- Misses       8860     8861       +1     
  Partials     1051     1051              

Impacted Files	Coverage Δ
cmd/argo/commands/get.go	58.89% <0.00%> (-0.88%)	⬇️
workflow/metrics/server.go	19.29% <0.00%> (+3.50%)	⬆️

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